Conferring lifetime status isn't necessarily even that expensive to the airline--you only get the benefits after you give the airline your money for tickets. It also creates an incentives to buy tickets on one particular airline, even when they might be slightly more expensive (which is the whole purpose of frequent flier CRM programs).
Now they no longer do that. So it makes the miles far less useful. And, since it doesn't apply to GS, all the other premiers still get screwed by this change. So it's not like it's gonna improve premier status for the rest of us anyways.
Ranty anecdote: Oh and they don't even respect what their ticketing and policies on this state. It was that any such ticket booked before 15 Apr would use the old rules, and indeed the baggage calculator would show that. Sent my sister somewhere, counting on some big bags to bring equipment. GA starts making a fuss, saying no, made her unpack and so on. Even after calling United and being assured she'd be treated properly on the return flight, nope, still not handled correctly and made to pay extra. United's IT is terrible. That's why we call their site ".bomb".
UA needs to get their shit together.
(quotes as delimiters; I can't find the exact quote )