I would have no doubts that AA's got in the background simulations run for the eventual matching of other partners with 1MM = Platinum, 2MM = Pro, and 3MM = EXP, along with CK at 4 or 5MM.

The most likely holdup is too many pre-2011 miles contaminating the system for now. AA does indeed have some numbers, they obviously know how many MMs you've earned since 2011, and from that, they can derive how many MMs are from pre-2011. They've obviously run the numbers on 4MM+ members who are active along with the ratios of pre-2011 vs 2011 onwards MM miles. I could bet that amongst the active crowd that would not otherwise earn PRO annually, the ratio of 2011 onwards MM miles is at a reasonably high threshold (probably over 50%). Amongst the much less active crowd, well, they've run the numbers to see maybe it's just a small handful of trips amongst this crowd where the incremental benefits they'd have to give out (+1 RDM/$ if paid fare, occasional OW Emerald lounge access (only a handful of airports where this makes a difference)) is negligible. SWUs are also no longer part of the equation, and any LT PRO or EXP earning these would have earned annual status anyways.

I bet each year, AA has a team re-running these simulations and eventually, when the ratio of pre-2011 MM miles is pretty much down to not much, then I could even see AA doing a tier realignment by promoting Gold and Platinum up a tier, adding a Silver at the low end, and moving LT EXP to 3MM.