For me and probably most users here, we have few rigs, I use Hive OS for free, only in 1 rig, and I have windows in another rig, because I use as my PC.
But can you imagine someone having more than 10 rigs for example, using windows?
It's a mess, you set windows to turn off updates and tweak everything to mine, and then windows make some updates, restart, have problems with drivers etc
That person can use Linux, but it's a long way to do everything, set a restart for GPUs in case they failed, or some problem with electricity, download drivers etc
With specific mining OS, everything is easy, in a few minutes you can set your cards, overclock, put the rig to restart after a crash, and you can monitoring everything in one place, it's the cost to this service you're paying.
I use Awesomeminer to manage my rigs, in my opinion the only good solution, because it is the only client server application for mining. You can use it with Linux or Windows (main application only for windows, but clients for both OS). I hate that these days all stuff run in browser, come on guys, it is browser and not a multifunctional tool to do everything.
I have build my own windows version 3 years ago, with this windows i need around 10 minutes to install windows with all driver that i need and so on, need only to type in the Rig name in the whole installation, nothing more. Updates deactivated for sure.