so the idea is this:
Disable achievements when there are mods installed. Achievements are meant to show off that you overcome various challenges that the game presented to you and show that you have some skills.
But with the use of mods, the game can become awkwardly easy. Hey, even the official modding guide shows how to make One-shot-one-kill revolver ammo.
bad idea
people can just use other tools to unlock achievments by cheating anyway, without even requiring the game to be open
so now you screw your legit players while cheaters can still get it just as easily, theres no reason
plus then someone would just make a mod to fix that anyway, it adds nothing and helps no one
people will cheat achievments and mods arent how most do it