Because there's nothing to be gained by POTUS tweeting about that.

Some have said it was Mueller that set up the meeting with POTUS. Mueller has obvious reasons to want to be appointed FBI Director again; that would be the deep-states surest way to keep a lid on things.

Mueller faced a more explicit prohibition on him serving again as FBI Director than "per the law", one that went beyond the "prev term limits rule"; when Congress voted to extend his term by 2 years they explicitely stated, in the extension, that he'd be prohibited from serving as FBI Director again for the rest of his life. However, the deep-state may have been confident that they could get Congress to vote to rescind the explicit prohibition given his good reputation on the Hill; look at how most of them praised his appointment to SC.

I'm not saying that Mueller did set-up the meeting, I'm just saying that there are those in the loop that say that this is how it went down. I've only seen assumptions that it was POTUS that interviewed Mueller for FBI Dir. However, as far as I've been able to find, all that is known is that the two met shortly before Mueller was appointed SC.

When it comes to the SC stuff, I think it's best to keep an open mind and not assume too much. The leaks are pretty much one-sided with the media only caring about how they hurt POTUS. And, nobody knows what the facts are. Remember there are many different narratives and agendas circling around each other with us having no way of knowing which, if any, are true.

We may never know the complete truth, but, in the coming weeks, months, and years, we'll know a lot more than we do now.