This might be a partial explanation why indie studios can be in meaningfully competition with the AAA-developers. They often integrate early and use beta, even alpha, early access. As a layman I find that approach more understandable. In my work, I always favore incremental changes to large process overhauls. We do have to understand that 10 years ago early access was a lot less common.
In the specific case of Celeste, the game was playable before development, because it was preceded by the PICO-8 version.
Valve did this a couple times by just buying out teams who made mods or interesting games - Narbacular Drop becoming Portal, that goo thing becoming the goo thing in Portal 2, Counterstrike becoming Counterstrike, then a CS mod becoming Left 4 Dead.
"Every big program that works evolved from a small program that worked" is even true for games