I think people are but it needs a mainstream celebrity or other mainstream public figure to endorse it. One of Twitter's old strengths. Storing nsec are going to be an impedance for some so it may even need a Twitter like front-end that entirely hides the underlying infrastructure. But, basically, private key management is going to put some off (erroneously IMHO). But needs celeb/public figure endorsement.

Whichever non controversial public figure is on here first gets close to 100% follows.