It is wild. And it looks like the NHL has only one in Scotty Bowman. So, why is this?
I don’t think a SC or SB win precludes the coach from winning with another team, it’s just that such coaches are usually kept. I’m sure if a SB/SC winning coach was forced to coach for a different team once winning one, he’d likely win another one. But, usually these coaches, who are heavily dependent on their QB (see Belicheck) and stick with them until they are done (see Belicheck). Plus, coaching 2 different HOF QBs in their primes is very unusual.