Alternative possibility (which, to clarify, is just a random idea of mine, not even a hunch): he sees himself as some sort of political figure, either as a candidate or as a kingmaker – just the position that, if I understand correctly, Trump has lost a few weeks ago.

For that kind of use, owning Tweeter, with absolute control on content and a user base stoked up on anger against "the Libs", "the pedophiles", "the establishment", "the deep state", etc. would be invaluable.