I'll point out here that the cheaper-than-average electricity prices that TX sees (according to the answer based on the Economist) is actually somewhat of a recent thing. Despite TX avoiding "the feds" for decades, for the 2000-2010 decade their prices mostly tracked the national average.
And as a difference graph:
(If someone can find comparative figures before 2000, those would be interesting for a fuller picture.)
Concomitantly with these price decreases in the past decade, spare generator capacity has also decreased in TX in the same time frame.
Since 2010, ERCOT’s reserve margin - the buffer between what it can produce vs. forecasted demand - has dropped to about 10% from about 20%. This has put pressure on generators during electricity demand spikes, making the grid less flexible, NERC said.
This was somewhat predictable, because the TX system pays only the generators that sell energy on that very day, which creates some perverse incentives from a reliability standpoint when prices are predicted to spike (why sell electricity today when you can sell it for much more tomorrow?).
Under existing market rules, the incentive for investing in better protection against cold weather is unclear, said Daniel Cohan, an engineering professor at Rice University. "To me our system of electricity is like selling lottery tickets," he said.
"Ninety-five percent of the year they're selling power for peanuts,” Cohan said. “They're counting on selling power at times like these when power prices spike 300 times their normal rate."
So, "race to the bottom" (in both price but also spare capacity) is basically the advantage (which you could put in scare quotes in that capacity regard) in recent times. Various advocates of this model have praised it (as recently as 2019) as the best thing ever: continuously decreasing overcapacity reserve was touted as an absolute plus with "naysayers" incapable of finding any concrete failures, according to said advocates. x
I know little about FERC, but I think they aren't actually in the business of regulating spare capacity in itself, as far as I know. In the post-CA-Enron-scandal days, it seems FERC were pretty/mostly concerned with companies manipulating and cornering a deregulated market, which however FERC generally advocated for. So, even being subject to FERC would in itself probably not avoided this pitfall of state-policies driven reduction in spare generator capacity. Nor being subject to FERC rules in itself seems to impede deregulating a state's electricity market to a large degree.
Apparently if a state (subject to FERC) does have a spare capacity market (which TX doesn't, but other states have) then FERC does get their say/veto whether the state's spare capacity market is operating fairly or not.
Alas, as FERC commissioner appointments are political, they sometimes break along political lines in such decisions.
The issue of FERC involvement in spare capacity markets however hasn't made the news much, compared e.g. to the more hotly contested issue of whether price caps should be imposed when the (regular) market is operating close to its supply capacity, which was a more salient problem in CA in the previous decade; CA seemingly had to lobby FERC for caps. TX basically avoids that kind of federal interference and e.g. ERCOT has been tweaking their price caps in the recent crisis, although it's a bit unclear in which direction, as they made several decisions in a short time span, some countermanding others. I haven't followed the whole saga, but apparently the end result was no to change to the price cap. However, I suppose that greater state authority/flexibility in such matters may be plus, as it allows faster decision making. (In the recent crisis, the ERCOT wholesale price climbed from around $50 to the ERCOT-set cap of $9000/MWh where it stayed for a couple of days, before dropping to $5. That $9000/MWh price cap was also reached in the summer of 2019, but for a substantially shorter period of time.)
More broadly, since 2005-2006, FERC does have a mandate related to grid reliability
Pursuant to the Energy Policy Act of 2005 (EPAct 2005), Congress expanded FERC’s role and jurisdiction under the Federal Power Act (FPA) by adding a new section 215 pertaining to electric grid reliability. Section 215(e) of the FPA authorizes the Commission or an Electric Reliability Organization (subject to review by FERC) to impose a penalty on a user, owner or operator of the bulk power system for a violation of a Reliability Standard. A penalty must “bear a reasonable relation to the seriousness of the violation” and must take into account the efforts by the owner, operator, or user to remedy the violation in a timely manner (FPA section 215(e)(6)). EPAct 2005 provides that persons and organizations that violate a Reliability Standard are subject to civil penalties of up to $1 million per day per violation, helping to ensure reliability of the nation’s bulk power system.
FERC actually delegates those reliability standards to the NERC:
Section 215 of the Federal Power Act requires the Electric Reliability Organization to develop mandatory and enforceable Reliability Standards, which are subject to Federal Energy Regulatory Commission (Commission) review and approval. Commission-approved Reliability Standards become mandatory and enforceable in the U.S. according to the Implementation Plan associated with the Reliability Standard, as approved by the Commission.
So I guess Texas power companies might be saving money by not having to comply with those regulations either, although Texas does have a non-profit org (the Texas Reliability Entity) that is part of NERC (not to be confused with ERCOT itself, which also has "reliability" in its name.) On the other hand, Texas RE does seem to a have a certain state mandate, but it's not clear to me if this entails that its members need comply with NERC regs/standards:
Users, owners, and operators within ERCOT are eligible for membership in Texas RE at no cost. [...]
The Public Utility Commission of Texas (PUCT) has authorized Texas RE to serve as its Reliability Monitor for the state of Texas and for ERCOT.
While one can find data on fines imposed by FERC due to failure to comply with price reporting regs etc., I'm not having much luck with data on FERC/NERC fines related to reliability failures or non-compliance. There's also one newspaper source which claims that being subject to FERC/NERC reliability requirements entails weatherized equipment, but I'm having trouble confirming the specifics on that.