Roleplaying?
Not every game option has to be the best option. Not every game rule option has to be a good option. In fact, some game choices are guaranteed to be BAD in terms of rules consequences, and people do them anyway because they want to play interesting characters. You can play a wizard with a 12 Int (I've done it, in the very first 3E playtest campaign, in fact). You can play a fighter who maximizes Con instead of Str. You can put ranks in Profession. You can take Skill Focus (Appraise). You can play a child, or a blind character, or a pacifist.
There are huge numbers of players who make and play characters that they think would be a fun or interesting concept. Players who don't worry about "optimal builds" to maximize AC or damage, because the game is designed for PCs to win and they can play characters that aren't minmaxed and not have them die all the time (I'll point out that the default encounter is CR = APL, which is an easy encounter that only uses 20% of the party's disposable resources... that's stacking the deck in the favor of the PCs).
The game expects you to have X gp worth of gear at every level. Deliberately choosing to play a character that ignores that and has essentially nothing at high levels is a very suboptimal design choice. You're allowed to do that. I think it's admirable for the people who want to play that sort of character. But it is unrealistic to say "because you've given up all these goodies, you gain other goodies that exactly make up for that choice which deliberately makes you a fragile character." And if you did build such a thing into the rules, it's basically saying, "you, the character that's made a sacrifice? It's not really a sacrifice at all, you're just as good as someone who didn't make that sacrifice. In other words, your sacrifice is meaningless because you're not really giving up anything."
If you want a game where all builds are equally viable, you should play a different game. Pathfinder lets you make suboptimal choices, or even poor choices, and it doesn't reward you for making those poor choices. Because rewarding poor choices is dumb. I don't see anyone clamoring that there should be a feat or vow or ritual for Int 8 wizards to get access to different powers to make up for his lack of spells, whether or not you call it the "Vow of Rincewind." I don't see anyone clamoring that the low-Dex fighter should get something that makes him awesome at dodging out of trouble and accidentally killing his enemies in comedic ways, whether or not you call it the "Vow of Jar-Jar."
I like the concept of the vow of poverty. It's a noble thing. And I understand that it sucks to be the impoverished character in a game where you're supposed to have 20,000 gp worth of goodies. So the VOP in UM gives you a bone in the form of extra ki. And another bone in the form of "you can have one item of value," which lets you put all your gp cheese in one item instead of ten. But I'm not going to let the rules make your impoverished monk as good as a regular monk. If you want to play a character that's making a sacrifice, make a sacrifice--don't pretend it's a sacrifice and expect a handout for pretending.
