Spam is an issue mainly because there are conspicuous meaty targets to be spammed, not in fragmented environments. And a target is meaty for spammers because that target has gathered, more often unnecessary, critical mass (large scale services, broadcast type news /thought leaders/influencers). Else even a small overhead for sending requests will drive away spammer incentive.

E.g. OS exploits were targeted towards Windows, not so much for so many of those Linux distros.