[pointlessone]

It's not too hard to build a decent detector. At one of my previous gigs (a niche social network) we trained a fairly OK NN to detect all sorts of undesired behaviours to flag content/account for moderation. We didn't even need that much data and training time for it to get OK.

In case of X its scale is the issue. Running the detector for every message, or even for every posting account once a month might be very expensive. This might be the primary reasoning behind the deliberation: make bots a little bit more expensive and finance the detector operation.