Quite likely a local optimum from the fact they a/b test everything incrementally all to heck. A major shift inherently will end up worse in the short term even

Quite likely a local optimum from the fact they a/b test everything incrementally all to heck. A major shift inherently will end up worse in the short term even if it is better in the long term. It's hard to do a major change both from the perspective of end user comfort and the fact it will need to be improved to deal with unforeseen issues.