Because game development doesn't work on a schedule, it never does and any date a developer can give you is just an optimistic estimate at best. Full disclosure here - I used to be part of a game dev company and I backed Drift Stage at the t-shirt tier and bought another shirt from these devs as well. And you know what? I'm fine with the pace they're at. Delays and missing deadlines always happen, and spending time to tweak physics - or at least that's what I think Chase is doing the entire time, is necessary because it's literally the core of the game. Anything can break down in a new build, sometimes the code just spazzes out because of different versions of " being used. Sorting these things out takes time. Making something multiplayer takes even more time.
And let's be honest, they took in our suggestions and kept changing the physics up to the last update - the one that reflected the overwhelming opinion for returning to the quick snap physics of the alpha and removing the snake boost. You'd be hard pressed to find many devs who are willing to step back down from their own image of what they think the game should be like and actually listen to players.
You know who didn't in recent events? Niantic and Pokemon Go. They removed everything fun about their game, made Pokemon harder to catch and shut down every site that set out to help trainers, even the ones that just let you check IVs conveniently. You know what they implemented in return for ruining anything fun to do in the game? They let you re-customize your character! Whoop-dee-fucking-do.
Anyway, my point is, Drift Stage, like every other game ever developed, needs time to polish and eventually give us new things to test. And in the meantime, since there's not much income after the initial funding, they need something else to fund continuous development. If that means new CDs and shirts, so be it. If you don't agree with this method, simply don't buy it. What else could they provide you if not just screenshots and hints of changes? Sometimes a change that was supposed to go through can't actually be done because of limitations in the engine or whatever, and if they promised this feature in a news tweet and couldn't actually deliver, you'd be even more upset and call them liars.