Steam Early Access is designed to allow potential community members to participate in a game's development - not to fund projects that may or may not fulfil their promise.
Although there are plenty of success stories, there have also been a number of Steam Early Access failures where the game has missed its release date by a significant gap; run out of money and tanked; or released but failed to produce the features players expected - Double's Fine's Spacebase DF-9 is arguably an example of that.
The service is garnering something of a poor reputation as a result of the negative experiences, and Valve isn't happy. According to GiantBomb, Valve has updated its Early Access rules and guide lines to make it clear what Early Access is about (bringing the community into the development process) and what it is not (a crowdfunding process for projects that may not make release otherwise).
There are four new guidelines that are especially worth noticing:
- Don’t launch in Early Access if you can’t afford to develop with very few or no sales.
- Make sure you set expectations properly everywhere you talk about your game.
- Don't launch in Early Access without a playable game.
- Don't launch in Early Access if you are done with development.
It's definitely worthwhile reading Giantbomb's full report to see all the nuance of what Valve is trying to communicate, but in short it seems that it wants to take the risk out of buying in during Early Access.