It leads to things like "people who tend to have to make important decisions have fewer clothing sets" ( https://www.businessinsider.com/successful-people-like-barac... )

I would contend that this is part of the reason why it is difficult for people who have to make decisions about "should I pay the rent, groceries, or utilities" to be able to join the white collar jobs - as those are about making decisions. If your will power budget is exhausted on food choices (because you don't have much money), its harder to make good white collar job decisions.

I would furthermore contend that the above is an excellent argument for UBI (though this gets deeper down into politics).

Don't you think this has a lot more to do with access? I can't imagine there are too many people saying: "I will turn down this high-paying management job because I spent my decision budget at the grocery store"

Access, I believe, is one part of the issue. I'm thinking more of the "my willpower budget is spent on the grocery vs utility bill" leading to other poor choices that make it more difficult to get a promotion that allows for a more care free life (not worrying about bills).

I believe that there are many parts of social and economic feedback loops that make it harder (and continue to make it harder) for people in environments that are willpower draining to move to jobs where the ability to make good decisions is the key value.

You could probably show that calories and certain other resources get exhausted by concentrated thought, however in my experience this has little to do with speed of thought and everything to do with depth (the only times I truly felt mentally exhausted was when I was trying to dig up deeply buried fragments of memory to solve a maths problem).