My guess is that it is a question about responsibility. In the trolley problem it is my responsibility to pull the lever or not. If I don't lose my money people will die. In real life it is the responsibility of everybody. Maybe still very egocentric not to donate but at least your conscience can let you sleep at night.
An interesting take on it is that if, for example you have 90.000 in savings you could choose not to pull the lever and use your savings to save 20 people in Guinea, but also this would not be a popular choice I guess.
There's also a matter of proximity. In many of the other problems, people chose to sacrifice more people that they didn't know well over sacrificing someone (best friend, cousin, yourself) that you do know well. The charity problem isn't quite the same as the trolley problem, because it's saving someone outside of your tribe in a faraway land, vs. saving someone who is presumably local to you and about to die in front of your eyes. Also note that people frequently do give up their life savings (in medical bills, or GoFundMe) to save people close to them.
The charity problem is also unimaginably complex. What if I donate my entire (literal) life savings...then lose my job, go homeless, and consequently die? I've thus saved a handful of lives, lost one (myself), and doomed maybe dozens or hundreds of other lives I could've later saved! Uh, whoops. :|
Every moment, every (in)decision you make comes at the opportunity cost of many other choices, and their exponentially multiplying secondary/tertiary/etc consequences.
These thought experiments feels like (#0) solving an optimization math problem where you're:
1. Stumbling through an unimaginably large solution space and
2. Latching onto local minima (heuristics like "choose the fewest trolley deaths"), which are probably bad answers, only to realize
3. We don't even precisely know the objective function we're optimizing. So the problem has gone "up" one level. We first need to solve that optimization problem. GOTO #0.
The whole thing feels farcically hopeless and is maybe even a recursive or self referential minefield. Yikes. So the idea of avoiding it entirely by just winging it through life using your gut, or checking out entirely, doesn't seem like such a bad idea. Hell, it might be the only way to keep your sanity. It's an unsatisfying heuristic, but...oh look, we're back at step #2... :))))))
An interesting take on it is that if, for example you have 90.000 in savings you could choose not to pull the lever and use your savings to save 20 people in Guinea, but also this would not be a popular choice I guess.