I'm guessing because Jon didn't get around to it yet.
Afaik, tmLanguage files (as used for source colouring etc.) contain language-specific rules for folding which are presently ignored by Sublime. Foldpoints from indentation is a bit of a cop-out, feels like a "quick and dirty" approach with plans to later improve with "proper" folding. It's a good fallback solution in the absence of any other lexical awareness; but since tmLanguage files have such info to hand I'm a bit disappointed that Jon hasn't seen fit to improve this for ST3, together with a facility for saving code folds within a project (or hot-exit) context.
The argument "sort your indenting out" is also a cop-out. It doesn't help at all when you're working on other people's code or following in-house coding guidelines at your workplace, dealing quickly with files whose formatting has been compromised, etc etc.. Ironically, working on others' large source files is when folding comes into its own. Folding as it stands is next to useless for me and just feels half-baked for now. Really hope to see this improve in the near future.