Because it is embarrassing regardless of the nature of the meeting seems like an easy defense.
So Trump knew of the meeting, and is embarrassed by it, and that's why he's lying?
So what is he so embarrassed about? He just tweeted "This was a meeting to get information on an opponent, totally legal and done all the time in politics—and it went nowhere. I did not know about it!”
That is not someone who's embarrassed. Your answer isn't plausible.