All of this is an exercise balancing information asymmetry and cost asymmetry. We don’t want to add more friction than necessary to end users, but somehow must impose enough cost to abusers in order to keep abuse levels low.
Unfortunately for us, it generally costs far less for attackers to bypass systems than defenders to sustain a block.
As defenders we work to exploit things in our favor - signals and scale. Signals drive our systems be it ML, heuristics, signatures (or more likely a combination). Scale lets us spot larger patterns in space or time. At a cost. 99%+ effective systems are great, but at scale 99% is still not good enough. Errors in either direction will slip by in the noise; especially targeted attacks.
As a secondary step, some systems can provide recourse for errors. Examples might include temporary or shadow bans, rate limiting, error reporting, etc. Unfortunately, cost asymmetry comes into play again. It is far more costly to effectively remediate a mistake than it is to report one. We’re back to cost asymmetry.
All of this is suboptimal. If we had a better solution, it would be in place. Building and maintaining these systems is expensive and won’t go away unless something better comes along.
tl;dr version: assholes ruin it for everyone.