The reason there is a discrepancy that arose your need to ask the question is because the question is based on incorrect understanding of what the media companies do.
All of the companies listed (not all media companies, but all the ones listed in the question), mainly function in one of two business models:
In this case, even if you care about US Government media buys, those buys are in the form of second business case, where US government merely acts as Yet Another Advertising Customer. In other words, they don't "fund" the company, they merely contract the company's service, like any other customer.
Additionally, as @Brythan's answer noted, they are not nearly a major revenue source for these companies and therefore, cannot exert editorial pressure on the company by threatening loss of business.
This contrasts with the case of companies like RT or BBC, whose major revenues source is actual budget allocated by their country's government - not in exchange for equivalently priced ads, but in exchange for content produced.
This is materially different in two important ways:
The content is what's being sold (not the ads between content). As such, the customer may - and often does - exert influence on what the content is.
The share of company's budget/revenue coming from the government is meaningfully larger, again making the government able to exert leverage on the content.
This is precisely why such labeling on Youtube applies to RT but not Fox/MSNBC; but it also applies to US media companies that are in part or whole government funded such as PBS in US or BBC in UK