You get the chance to get a game you obviously like the look of, at a generously discounted price.
It is all entirely OPTIONAL, if you do not like Early Access, wait till the final release, lookup other player reviews and pay more money if you like it.
Or, just pay the money and do not touch it till the game is "gold".
Some "niche" games I like would never have saw light of day without such options of early/alpha access so I am happy.
ALSO...
A £40 game from a "AAA" publisher which has been internally "play tested" etc can sometimes be MUCH WORSE than an Early Access title by a small dev team.
The AAA publishers really have ****** up the public perception of what "Beta" actually is.
A "Beta" does not happen 4 weeks before release as an incentive to pre-order.
A Beta is generally feature complete but is not feature locked. Alpha, possibly unplayable at times.
In relation to Early Access specifically, the ones I have purchased state plain and simply "Game is playable but broken in certain parts" so I know what I am getting but I would rather have that choice than not at all.
Lets all go back to the publisher only route, that worked out really well (Sarcasm).
This route allows developers to develop independently using their own ideas without some idiot publisher/money man who knows nothing about games in a suit saying "can you add infinite respawns" etc etc.
Sure, some games may not turn out as the developer intended, maybe as a game nears completion, it is discovered the "game" does not work as intended when everything is fused together but that is not known till it is made. That is the gamble, if you do not like such things, YOU DO NOT HAVE TO SUPPORT THEM, WAIT TILL FINAL RELEASE.