A person who "fell on hard times" has at least in theory had the chance to try to save past income, and has a realistic prospect of earning higher income in future, assuming the BI is insufficiently generous to dissuade them from seeking paid employment altogether. Given that the average annual income of an able bodied person over the course of their life really ought to be higher than that of a too-disabled-to-work person, it doesn't seem unreasonable to redistribute less money towards their needs in a period when they're not in work.

Which able bodied person should be the ceiling on too-disabled-to-work people's income? Not sure, but I'm reasonably confident that "the most unambitious and indolent one" is not the correct answer.