As others have said, churning has gotten more popular and so it stands to reason that banks are finding ways to crack down. I don't think the trend will reverse itself, at least not in the foreseeable future. Churners and/or people signing up for many cards just to maximize rewards (even if they aren't technically churning) are not really profitable customers for the banks, so they don't care as much about gaining or keeping them. Banks would prefer you just choose a card (with them), use it and stick with it. The more cards you hold, the less likely you're going to put significant usage on their product.
Pretty much every large bank has some type of policy now, some more lax than others. Chase's is definitely the most strict, but the general population is not opening 5+ cards in 24 months (unless they are churners or credit hungry and that's a whole separate issue), so again, the people who are locked out are the ones Chase doesn't want anyway. Sucks, but it makes sense from a business standpoint.