I think if you pay cheap salaries, manage to wrangle some high performing talent together, and spend enough time working on something interesting - you're probably looking at $250K-500K minimum in expenses to produce something beyond a "toy" or a "tech demo". As a studio founder I don't mind fronting some, or all, of that money if I have a feeling the game will be a hit and make that back.
Right now if I had a 100% buy rate (every single person that bought a Vive also bought our game at full price) we'd be struggling to break even right now. That's the reason why big players aren't in the game yet - your best possible case scenario is losing money.
Other than finding investors, making deals with platform holders is the next logical step. Theoretically speaking only, Valve could offer us $100K up front to put the game on their platform - and they could offer $300K if we made it exclusive to their platform.
Suddenly as a studio head I have to make a very tough call. Do I halve the size of the team, or gamble and go into debt and take the non-exclusive? Or do I make this a "sure bet" and go with the exclusive?
Business-wise, exclusive deals almost always make sense. The numbers they offer are designed to be very tempting - they've done the math, they know your team size, and they know what the market is likely to generate. Exclusives completely remove risk, and that makes those deals very attractive. The platform holders, meanwhile, get yet another selling point to hopefully put them "on top" in the market. Win-win.
From the consumer point of view, exclusives are annoying, fracture the marketplace, and generally seem like a jerk move. I also understand that some games would simply not exist without them. I personally wish platform holders offer exclusive levels of money for non exclusive deals, but that's not likely to happen.