I'm not sure! The game unfortunately does need to have some kind of end condition. It's possible climax blocks aren't the right answer, you're right it's sometimes frustrating when it feels like they show up too soon. A sandbox mode would be interesting, I agree it might be fun to just build a combo forever and set it off whenever you feel like. But it might also feel anticlimactic when you set off your huge 1,000-block combo and the game just asks you to continue playing.