Majorca is still popular after high summer (and sunny!)
The Balearic season starts in earnest on the 1st May, and half term at the end of May is a major demand period. As I say, it’s the start date that’s slightly odd, not the end date.
While the no-frills carriers are less likely to slavishly follow the traditional aviation season schedule change dates, and to commence and suspend routes on those dates, they do tend to follow a pattern - keeping ski routes going into April; increasing frequencies to Christmas Market destinations after October half term and until the ski demand picks up etc., etc.
So, there’ll be a reason why the Ryanair routes aren’t starting until June, which is unusual for anyone, and joking apart it’s likely to be resource driven one way or another.