PC/Console games take massive amounts of man hours to make and as I see it the point of Early Access is to give smaller Indie Developers the funds to hire more people and get the entire game made in an achievable time frame (though some of these things still take almost a decade to get there).

It's a bit like Kickstart, but for Early Access there needs to be enough of a product to appeal to gamers (and hence quite some time invested into creating it up to that point, plus a decent idea and an actual game play which is deep enough and has at least a good enough basis of gameplay design that it's actually fun to play), which also means scams are far less likely because just getting the game all the way to a level that qualifies it for Early Access is already quite the investment in time and possibly money plus worse comes to worse and the developer stops development immediately after caching in with Early Access, buyers still got themselves immediatelly a small game at a cheap price, though not the "dream" full game they were promised they would eventually get.