Because the kind of people that tend to make indie games don't have the money to keep themselves under a roof and fed without taking gainful full-time employment, which gets in the way of getting a game out in a timely manner since it's done purely in free time. The investors don't want to make it into a grant a) out of respect for the developer and transaction and b) because they don't have oodles of money themselves, at least compared to more traditional investors.

Think of it less as a business venture to jumpstart a company and sell it for millions later and more as a way to allow people to have a job doing what they really want to do full-time... so long as the game is successful enough. :)

Understood. Then it's more important to spell out the terms of the funding ahead of time. Are they paying you money to develop the game then take over the end result completely? That would be 100% equity funding and it sounds like a "job" to the dev. 6%, 10%, 20%, 50%?

The aim is ramen profitability, I guess.

Vague outlines to the funding terms are at http://indie-fund.com/about/ . Basically you pay back a proportion of revenue til you pay then back plus a bit. Or, if you make no money in the first 3 years, you don't owe them anything.