This isn't a devaluation of points, but a new barrier to earning points.
Chase, by far the largest issuer of points and miles credit cards,
has started cracking down on people who apply for new cards too frequently. From the Wiki of
this thread:
Starting in May 2015, Chase began denying applications for its own branded cards (e.g., Sapphire Preferred, Freedom; but not United, Hyatt, IHG, etc) if the applicant's credit report shows that she or he opened more than 5 credit cards in the past 24 months. The count includes cards opened at other banks and even cards on which the applicant is only an authorized user, not the primary cardholder. Chase has been extremely inflexible with this policy, with agents stating that there is nothing they can do to circumvent this restriction. However, in some cases Chase may reconsider a denial if the applicant has <6 new cards excluding cards on which s/he is an authorized user.