Most people play with either 3-click or controller because it is so easy to hit.
Not sure where your data on "most" is coming from, but I can say that I certainly don't play RTS-C on PG Tour Pro because it's "so easy to hit" (it isn't).
Personally, I play controller because I enjoy playing exclusively from the couch these days with an HTPC and it's also wonderful to have all game controls right in hand.
I'd actually built a lap board thing and played MS at the couch before RTS-C came along and it was ok, but just a pain to set up and use and involved a lot of crap hanging around in the living area that wasn't appreciated by the household, nor could I lay back and chill like one can with a controller.
Anyhow, just an anecdote I thought I'd share.
It's a touch presumptuous to assume that "most" are using 3C or RTS-C because it's "easy to hit" (your words, not mine).