Are those changes the cause of increased profitability, though? Yes, they do provide a higher level of recognition/miles to high spenders, but do they bring in more revenue versus just reallocating the miles awarded for travel?

Unless AA can demonstrate that their current program is causing a significant loss of revenue compared to the competition, and that a new program will rake the dollars in, they may find there's not a good reason to change anything.

Once you make a change like UA or DL, it's not going to be easy to reel it back in if you find it was the wrong call and your mid-tier and lower-tier flyers bail on you. AA seems to be working around this now with bonus miles on some fares, and maybe that's the route they'll continue to pursue.