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It's just bad practice. There are other locations suited for program data / application data.
But devs often ignore the rules.
That is why "My Documents" was NEVER "my" documents, but a place where some devs put THEIR stuff, and other devs put folders for my stuff.
I realized back then that the only folders that were MINE were ones I created, preferably on other drives..
That holds true even now, although I allow most programs to assign my files to "Documents", those that I care about i move and symlink.

As far as creating folders in the root of C drive....
There are many devs who do it, and it has been for the most part despised by people who like to manage their own computers.

System builders like Dell, etc have done it as a way of keeping their files seperate from all others, and for good reason, as they often contained important files to restore systems, etc.
Other cases are not so forgivable.
Intel has done it for a long time (as a hidden folder), but also some backup utility devs (EASEUS, for example)..

But even Ret, a hacker who ought to respect peoples' "C:\<root>", placed a folder there for Gullfoss.

Well, a lot of people don't care. A lot of people have no idea where the root of their C drive IS to begin with...
But for some of us ... perhaps a bit OCD ... it's an unnecessary intrusion.