Matt Levine had a pretty different take, pointing out that if Elon Musk suddenly appears to be unwilling to buy Twitter, his financing might see that and - suddenly, but perfectly legitimately - evaporate, which would be a valid reason for Musk to walk away.
It really is true that lending someone a lot of money to make an investment they aren't interested in is a much worse financial move than lending the same money to the same person to make an investment they are interested in.