The $2000 number is a cap for wealth, not income.
The problem isn’t having a phaseout or not anyway - we could set a wealth cliff of $50k and that would be perfectly fine. It’s the numbers that matter, where the phaseout or cliff is placed and how steep a phaseout. $85 a month is a redonkulous place to put the phaseout even if phaseouts are “better” - that is a worse policy than a 50k a month cliff!
And you’re right, the reasons the number hasn’t been adjusted since 1935 (in 1989 the number was inherited from a prior program, it wasn’t adjusted at that time) is because of political will. Social spending on anyone other than the elderly is extremely unpopular in the US.
I honestly don't care if $85k is the cutoff. I don't care if there is a cutoff at all (but I recognize some people don't like the idea that if a millionaire becomes disabled he'd be eligible for some amount of money from the government). If someone becomes disabled or whatever, and they have money saved from working, why would they not get benefits? Why do they have to deplete their savings first to get shitty benefits? Social security doesn't have an income or asset cutoff; why does disability?
I actually personally agree with the sister post of just...paying people based on their disability, without caring about how much other income they're able to generate, or assets they collect. But I recognize how politically untenable that is.
Suppose that between $25,000 and $35,000 income, you start paying taxes, you lose food stamps, you have to start paying toward your medical insurance, you lose your daycare assistance, free school lunches, etc., etc... each one of those could be staggered, but the net result is just overwhelming.
I'm not a big fan of social programs; but if we're going to do them, they should at least be done sensibly.
It's even simpler: stop means testing individual programs, that's what progressive taxation is for. If you are going to give someone benefits due to a particular level of disability, give them benefits calculated based on that. If they have more outside income than you would expect with that disability, good for them, and they’ll also pay more taxes. Same with other special-circumstance aid qualifications (for general poverty support, this reduced to UBI.)
Neither the group that needs help (and their supporters), nor the group that doesn't want to give hands out to people who refuse to work but could, have reason to object to something like that.
The actual problem is the red meat that welfare/socialism is to our political bases in the US, and the incentives of politicians, on both sides of the aisle, to ensure it persists. If you do the obvious thing to actually address the problem, neither side can use it any longer to stir up the base. So the incentive is to not actually fix it.