Not explain why they are broke, but rather why they are not retired.
I had a PC once who took his first biggish haul and opened up a shop that sold eclectic goods. I hired people to run it while we were away and paid well to inspire loyalty(less theft). They bought and sold items to make money, but I also used it to sell the magic items and goods that we acquired adventuring. I mean, why sell to a merchant for half-price when I could sell it through my store and get full price(minus shop expenses)?
Again, we're on the same page here.
Yeah. Spellcasters are fairly rare in my game. If the PCs go to the main temple in the entire Forgotten Realms for a major deity, the high priest will be a cleric with double digit levels(or the 5e stat block equivalent), and there will probably be 3-6 more clerics there of lower levels. A lesser major temple's high priest MIGHT have low double digit levels(or 5e stat block equivalent) and 1-3 lower clerics. A medium temple probably has 1 single digit level cleric and MAYBE 1 other cleric there. Shrines and lesser temples may not have a cleric at all. Acolyte background priests are 99% of the priesthood. Wizards are similarly limited in number, and sorcerers rarer than that since they are bloodline related.
I was never even really all that convinced by the whole "a hierarchy of guys with higher levels runs things" conceit that old time D&D seemed to imply. I mean, it serves a couple of purposes in a sort of prototypical D&D campaign, but it nothing like what would ACTUALLY happen. Look at the real world, the Dean isn't some prestigious researcher, he's the guy that knew how to kiss ass with the Board of Regents. He's probably the equivalent of D&D's 3rd level Magic User, he's bona fide, but not extraordinary. Likewise, how would the King have learned the awesome skills of a 9th level fighting man? Like where? No, he probably doesn't even know how to use a sword! And so on and so forth.
I mean, sure, its heroic fantasy, or some fairly adjacent genre, so we of course roll with it to a degree, but still... Yes, in my last full up 4e campaign there were SOME high heroic tier figures, here and there, though mostly not politically or organizationally powerful figures in most cases. If there is ONE PARAGON in the whole land, well, that's pretty much what paragon means... Epic tier guys? Nah, they are the ones that bards sing about when they sing the classics, most probably lived 1000's of years ago.
I never really dug the equating of wealth in a conventional sense with other sorts of achievements either. I mean, 5e at least doesn't seem to care about that much. 4e just basically made wealth meaningless anyway, and then let you play with lots of 'gold pieces'. Honestly, its probably a reasonably solid approach, overall. Anyway, in a world where dragons eat your gold treasure hoards, chances are the world mostly runs on barter anyway, lol.