Most of the listed shareholders were shareholders in Twitter well before Musk bought it - in fact, it was during Twitter's IPO roadshow.

For example - DFJ (2010), the Al Saud family (2011), and Fidelity (2011).

In this case, these are minority investors restoring their ownership stake.

IMO it was a pretty good gamble. Even if his mental decline seemed obvious, it wasn't obvious they would be prying X from his cold dead hands at all or nearly this late.