I have today massively reduced the natural spawning of ZombiePigmen that happens around Netherportals outside of the nether. The issue is that some players built huge arrays of them to spawn thousands of pigmen and harvest them in automated machinery. Now there is a by-lot maximum cap of 10 pigmen.
I disabled those for the same reason I disabled IronGolem and Villager farms. The simply allow you to automate things in the game that turn it into a creative-mode like system. While these spawning methods were initially meant for the single-player experience, users can get together and built far too effective systems that let you harvest too many goods in a too short time and often create heavy lag at the same time.
Nether portals for example cannot be switched on & off automatically, and an unattended system would spawn hundreds of mobs in one lot in a very short time. So I hope you all understand that I switch those off. I know it’s fun to build these automatons, specially the big ones. But they destroy the server economy and the survival gameplay.