This should be explained on the front page of Colemak.com, it's asked so often!

If you swapped R/S, you'd end up with FR and CR (which are both common bigrams) on the same finger. Same-finger pairs like that are considered bad - once your speed is up, you really start to notice them. On the other hand, SF is extremely rare, at least in English.

I agree the S thing is a pain though, it put me off initially too. You do get over it though. And when you do, you also get to enjoy typing words with ST.

Other people tend not to get the layout changing thing. Most people just accept what's in front of them and don't care about the inefficiency of Qwerty. It's only people who are perfectionists and/or independent minded that are willing to take on the challenge. Weird though, in most jobs, using the best possible tools is considered professional. But despite people spending large parts of their working life in front of a keyboard, so few people care about either its efficiency or comfort.

BTW, regarding "people spending large parts of their working life in front of a keyboard". Keyboard as a device is declassified to the low-cost addition to the computer, no matter what it is, it should "just work". Most people find funny the idea of spending some noticeable money for the keyboard. This is not as cool as spend money for some modern computer part which is really seen as they affect the computer's performance. I had the same attitude before as well. But now, after discovering mechanical keyboards, I will never use the cheap office keyboard again. Quality change is incomparable, this is like use all your life a cheap car (to move from A to B), and one day switch to Mercedes (which is also move you from A to B, but waay more comfortable).