You still don't get it, you pre-ordered Baldur's Gate 3 game and as a BONUS you got early access version of it to get a little taste of what's to come. Usually you don't get anything when you pre-order a game, but Larian was so nice to let you have a little taste of what you will get when the game gets released.
You make is sound as if Larian were doing players a favour. It provides them with data and testing ground, (and upfront sale!) and and more passionate fans can test the unfinished game, provide feedback and act as guinea pigs in hopes to make the final product better for everyone. It is also a bit different as pre-order as you might not be able to get a refund before the game actually releases - you just buy an unfinished game, in hopes it will be good one day. It's a business and development model, and arguably one that puts a bit more risk on customers part then I would like - though in times of liveservice games, Larian is honest about what they are selling - and unliked most live-service games, I have a pretty strong faith in them finishing the game. More importantly, one doesn't loose anything by waiting for Larian to finish their work - and that is a key reason, as I mentioned, against adding anything extra for EA. I think it is fine, if it's a clear mutual-benefit arrengment. It's less fine, if devs try to aggresively sell the game before they finish making it.