This is true, and I did think about mentioning that but decided to keep it brief because once I start talking about trusts I’d find myself out of my depth pretty quickly and probably open up a rabbit hole of other financial strategies I’m not prepared or qualified to go down (and also to keep my comment at a more readable length)

But since we opened that can of worms (and like I said, this is getting out of my depth, so there’s a very real possibility that some or all of what I have to say after this is wrong, so take it for what it’s worth)

We also don’t know how much money we’re talking about here. The line between qualifying for benefits and not can be razor thin sometimes, and while we might assume that we’re talking about 10s or 100s of thousands of dollars or even more where a trust would absolutely make sense, we might actually only be talking about a couple thousand bucks, maybe not even enough to afford a couple months of rent depending on where you are, but potentially enough to fuck up someone’s benefits depending on where some government bean counters drew the line. It might be difficult or impossible to find a financial institution willing to act as a trustee for such a small amount, and there may not be any individual they trust to fill that role, and once the lawyers and such are paid there may not even be much left over.

There’s also the possibility that the parents are counting on the sibling(s) to sort of act as trustees without putting it in writing. We don’t know what their relationships and personalities are like, or what conversations they’ve had with their parents that maybe OP isn’t privy to. There could be an understanding there that they’re getting everything so that they can continue to provide for their disabled sibling after the parents are gone, and OP hasn’t been made aware of that (some people are really uncomfortable talking about this kind of stuff and avoid it even though they really should) or misunderstood what the intention is. That of course depends on the siblings being trustworthy and generally having their shit together well enough, which isn’t a given of course and their situation could change drastically.

There’s also the possibility that a trust is exactly what’s happening and OP either misunderstood it or just plain doesn’t like it. A lot of people out there are pretty clueless about financial matters. If the siblings were named as the trustee (it’s often not a good idea to have the trustee be a close relative, but that’s neither here nor there) I could see some people viewing the situation as “they left all the money to my siblings” because they’re not getting a big one time payout and the money has to go through their siblings in some fashion.

Again, I’m talking all in hypotheticals, there are countless “ifs,” “ands” and “buts” here, we don’t know the specifics of OPs situation so we can only speculate.