He looks like he has enough of a stranglehold on the nomination that he can get away with this. Furthermore, as has been noted, the less people there are, the harder it is for him to get away with his lack of knowledge on subjects with hardline bluster and general Trumpiness.
And when he doesn't show up at the convention with a majority of delegates, the fact that he skipped two debates will be used as one more nail in the coffin of why he shouldn't be the nominee. "Donald doesn't care about the party, just his own ego." Or something like that.
