Centurion lounges is a feature that Chase and Citi apparently do not have the budget to match...
I disagree, I'm one to believe Chase and Citi have more money to spend than AMEX does at the moment. Both have more product offerings and cards that are just as good, if not better than what AMEX offers. Perhaps Chase doesn't see building their own lounges and selling their use to their customers as a significant business advantage at the moment.
If the largest bank in the U.S doesn't have the budget to build a competing lounge network with a relatively small bank [Centurion] with credit cards as their main business along with very few loans and savings accounts, then there's a problem.