The deal at $54.20 was maybe OK for him a month ago (it was great for Twitter because nobody else was interested at that price). Since then, Twitter reported disappointing numbers for the past quarter, and the entire market took a nose dive, with tech hit especially hard.
TWTR stock price was in the mid-30s before Musk's offer. Without the offer, and with the disappointing numbers, and with the recent market development, one could reasonably assume that the stock would be below 30 today.
Musk should just pay the break fee of $1bn, and renegotiate for $42.69 or whatever meme number he fancies. Why pay $42bn total for something when you can get it for $30bn.