Because we already know from his past behavior that he's willing to make long-term bets. And his statement that he doesn't view his interest in Twitter as a money-making venture.
> He sued Top Gear because of a somewhat negative car review of the original Tesla Roadster
That's a very biased way to frame it. IIRC Top Gear admits that they faked part of the review to make Tesla look bad, after Tesla proved that they had.
Believing in free speech doesn't mean you can't sue people that you believe have violated laws.
Or perhaps he simply made a mistake of judgement going after them legally and was wrong to do so. That's also not inconsistent with a belief in free speech.