It appears that Universal's new Season Pass Plus offers more weekends in May and June than the outgoing CA Resident Plus pass. Perhaps they're projecting low numbers for June, and they're longing to get more guests through.
All in all, I'm somewhat shocked (but ultimately not surprised) they haven't settled down on a system after all these modifications. Constant change like this is bad, and it simply frustrates and confuses your customers. Even with all these reduced tiers, they still have more annual pass options than their competitors - all at the expense of what? Are they simply confused, or do they lack decisiveness?