Yeah, after the clarification, it really sounds like your DM is ignoring the RAW for wealth by level, and you're feeling the pinch. I'd start off just by calling it to his attention: "Hey, the rules say that we should have X amount of GP wealth, but we only have Y. Is there a reason you're keeping us this poor? Cuz I gotta tell you, fido quests and such are fun and all, but it's all we've been doing, and it's not bringing in the bacon like it should."
If he becomes intractable, that's when you offer to run your own game and see what the group has to say about it.
But D&D is the sim fantasy business, the business is adventuring.
The RAW isn't written to treat adventuring as a business, but rather something like winning the lottery -- you loose, you die, you win, you get rich. It's more contest than business.
How many adventures involve getting something for somebody else so they can make money? How many involve escorting caravans? Most any adventure that doesn't stick it to the PCs by expecting them to do something out of the goodness of their heart, has them working for a patron.
Yeah, but eventually (especially when cusping high level, especially in a setting like Eberron where you're truly unique individuals at that level) you stop escorting caravans through the orc tribe's lands, and start tackling the orc tribe itself. You stop needing to get something for someone else, and start doing it for yourself. If you're 14th level, in Eberron, there's precious few other characters who can do what you do, and most of them are inaccessible. Guarding a caravan is something of a waste of your rescources.
That patron is probably making much more money than the players are collecting. However, the jump from working for a patron, and becoming the guy making the money, is a hard one for DM and players alike. Most DMs would rather not have the caravan guarded by the PCs be the PCs investment and business windfall. If it were, chances of the caravan ever reaching its destination or making a decent profit would be much less, I suspect. The adversarial DM shows up much more often in trying to keep the PCs broke than actually trying to kill them off.
Business bookeeping isn't exciting for a lot of people. The intricacies of fantasy economics aren't something the game is meant to dwell upon. They're a means to an end -- a way to get the PC's back into the dungeon, facing more vile threats.
Judging from the clarification, the OP feels he *has* to do this in order to profit, because the adventures aren't paying what they should be paying. In other words, he wants the adventure, too, but is finding that the adventure isn't giving him enough incentive to stay interested. And the DM isn't giving him other options to pursue his interest (probably because the DM assumes that 500 gp for a fido quest is just fine).