The installer only allows you to install it on c anyway doesn't let you change the install path and the internet doesn't tell you if there are any cmd line switches to install it on another drive so I guess it does matter after all although there's no reason you could have a c drive that develops errors just as much as any other drive it has to load on startup so maybe if it was on a slow or different drive it's just to keep it organized because if it was on different drives and a drive failed then it might hang the system on startup or something who knows looks like samsung just hard coded it to stop you doing anything silly.
Well actually it doesn't even have to load on startup you can just open it when you want to use it so whatever maybe because they think it accesses the system it should be hosted on the os drive but it should also be crash resistant your pc can crash while samsung magician is running without rekking the drives, for another reason. nobody really needs to know why exactly I guess.
If you ever had a bsod or reset your pc with the reset switch or just turned off the power at the wall socket without shutting down, or had a power cut well maybe it might break something if you were in the middle of an operation like setting over provisioning but that still isn't a clear reason for only having it on the c drive. If your system crashes for any reason that's still not a technical reason to only host magician on c.