Twitter's success wasn't due to "enforced terseness", it was due to the fact that it supported posting to it from SMS messages back when the majority of the population still had dumbphones. Once smartphones became ubiquitous, Twitter kept riding that wave due to network effects. In fact, the entire reason for the 140-character limit was so that it could interoperate with SMS cleanly.

I do somewhat agree with your overall point though. And it's worth noting that sometimes that "new feature" can be things like "my parents don't use it yet", in the case of teenagers and the like.