When I first discovered Kerbal Space Program, I found it was great. And then I discovered the mods; and they turned a great game into an amazing one.
About 70 mod installs later, I realised that installing mods was time-consuming, and error-prone. Each mod seemed to have its own set of dependencies, its own way of being packaged, its own way of being installed. Worst of all, some mods would conflict with each other, something I'd often discover after it was already too late.
I saw the same problems were plaguing mod authors as well. Users would be asking for help because they had installed the wrong version, or were experiencing conflicts with existing mods.