Yes, he was forced to buy it ... after he initially signed a paper committing to buy it. He was only forced after trying to get out of what he had signed.
It would have cost him "only" a $B to weasel out, much less than expected losses. So it has value to him greater than those losses. Would be unsurprising if he used it for political leverage. I don't think he is allowed to run for the presidency, but he can probably seat his choice.
This is a common misunderstanding. The $1B clause was for if the deal was blocked by regulators, it had nothing to do with Elon just deciding to back out of the deal, so just paying that to walk away was never an option. The commenters above saying that the court was about to order specific performance have it right.
(Reverse) break-up fees are a tool to ensure commitment of both sides to a deal. The main target in the Twitter deal was probably the financing, not the regulatory case, making it a bit less attractive to fail the financing for the deal somehow to get out of it (although there was some debate how realistic that option was anyways). And in the other direction, Twitter was on the hook for a billion for various things it could've done to hurt the deal, e.g. the board recommending shareholders vote against it, or for a competing offer.
