It has recently been reported that King Charles benefits from the estates of those who pass away without leaving a will or next of kin. Apparently this takes place via ancient feudal laws known as "bona vacantia" that allow the King's duchy to inherit from intestate individuals.
Presumably this is not likely to be popular even with Tory voters. So how come the UK government does not update the laws and close this loophole on the basis that it is likely to harm their electoral prospects?
Property with no other successor has to go somewhere.
The amount of property at issue is modest. It is about $7.5 million USD a year (in an economy with a GDP of $3,131,000 million USD a year), which is about 9 pence per person per year, and the King has pledged to donate all of it to charity anyway.
Anyone who really cares about where these assets go can prevent the escheat of their assets to the King by writing a will (which need not be very expensive).
Indeed, the threat of that possibility probably generates significant income as a marketing bullet point for solicitors trying to encourage people to draft wills (see, e.g., here), which probably creates low key political opposition to change from the fairly influential barristers and solicitors lobby.
In the case of monarchists, especially Tories who are members of the historically most pro-monarchy political party, reforming this practice might be perceived as anti-monarchist. This is because a change would directly harm the King's personal financial situation (should he cease to donate it to charity in the future), and because it would indicate a lack of trust in how the King choses charities to benefit from it. But opposition to the monarchy is an impression that the Conservative Party would like to avoid.
And, people "who pass away without leaving a will or next of kin" are not know to be a powerful political force.
All of this adds up to little political enthusiasm for changing the status quo.
Also, reopening the issue could lead to intense fights over who should get the money instead. This would invite unnecessary conflicts between interests that are otherwise not at odds with each other. Few politicians are interested in creating political problems for themselves of this kind that they didn't have before they poked this hornet's nest of a political issue.
Not to be entirely tongue in cheek, but before the practice of bona vacantia was established, in Bronze Age and Iron Age Britain, "taking it with you" by having many of your significant possessions literally buried with you in your grave as "grave goods" was as a common practice that solved the problem in a different way than we do now. And, I don't see a lot of agitation for a return to that practice.
So, the UK is weird. Officially, parliament advises the monarch, as head of state, to sign the bill put in front of them, at which point it becomes law. Technically, this can be refused. However, if it is refused, parliament is likely to pass something removing the monarch from power.
To stop this from ever happening, because this is pretty much an automatic constitutional crisis, even for the UK's unwritten constitution, laws that affect the royals are vetted by them first. The guardian reports here that this procedure has been used by the royals to suggest changes to a wide range of bills before they were debated: https://www.theguardian.com/uk-news/2021/feb/08/royals-vetted-more-than-1000-laws-via-queens-consent
This also helps MPs avoid the other issue they have, which is that they swear to "be faithful and bear true allegiance" to the reigning monarch, as a condition of taking their seats in parliament (incidentally why Sinn fein MPs do not sit in parliament). Harming the King's financial interests might be seen as a breach of this oath.
It is even more complicated by the new king - Charles is less well respected than the queen was, he's seen as more outspoken (bad for an unelected head of state whose job is, essentially, to wave and sign things). MPs could be pretty sure how the queen would react (she's signed worse things) but less sure about Charles.
This is all pretty arcane, and, if there was political will to do so, it would be possible to pass something altering this law. But it's treading on tricky, ancient constitutional things, with a new king who no one is quite sure about, making it almost certainly a minefield no one has any interest in entering. All for only £6 million a year, which according to the king goes to charity (although it seems to largely go to enriching him at the moment)
A point not mentioned in the other answers is that this only applies to parts of England - the territories which once formed the Duchies of Lancaster and Cornwall.
So as well as the limited political impact of the distribution of assets of people who both failed to write a will and had no identifiable next of kin, it's not affecting Scotland, Wales or Northern Ireland, or most of England - parts of the North West and the extreme South West.
Bona vacantia goes to the state, with the exception of the Duchies of Cornwall and Lancaster where it goes to the monarch's estate.
The state funds the monarch anyway (as their salary, to fund residences, etc). If the proceeds of bona vacantia were all directed to the state, the state would have to fund the monarch equivalently. Effectively bona vacantia just cuts out the middleman - you can think of it as merely a different accounting line on the spreadsheet.
Therefore there isn't much practical difference in terms of abolishing the right of the monarch to benefit from it, besides rejigging the spreadsheet.
