Operating a spam network has a cost too. The incentive to run spam software is making money out of it. Annoying spam does not sell, and non-annoying "spam" is really spam? or just advertising?, which we're not entirely against.

Besides, this problem you're describing already exists on Telegram, for example. But people keep using Telegram because the benefits outweigh the downsides.

"Trollbots" do not have an economic incentive, and ignoring them effectively makes them pointless.

Also economic incentives work both ways. Their principles work on the side of the "victim" too.

"Trollbots" might become an issue, not for regular people, but for "influencers" mainly, but "influencers" already have an incentive to keep their feed clean - they can make money with it (well, some may prefer just the ego boosts, to the same effect).

In which case, they can simply run an AI bot that they pay for a few sats to clean their feed for them in real time.

As you can see these problems you're pointing out are all self-regulated.