That's a real phenomenon and it certainly isn't limited to diving.I was told by a many people that the reason they did not go professional is because they would stop enjoying diving as a hobby. Many people told me that they started to look at their professional undertakings as duties and stopped having fun.
My opinion is that DM is only for folks who want to trade their time to a dive shop for boat rides with customers. AFAIK you don't get paid to be a DM, so it's really just a stepping stone on the way to instructor OR it meets your need for that trade. If you're someone who just likes helping others, DM is still a stepping stone on the way to instructor.
Most shops also expect their DM's to sell dive crap in a store, in addition to actually divemastering. I'd be insulted if I ever encountered this.
Now.. some people just like the extra dive training. If you throw away all the "business" stuff they teach in a DM course, you get a bit of that from DM. You'd probably be better off taking a master scuba diver course or getting into technical diving if this is what's driving you.
Don't get me wrong. I like DM's. They haul my heavy tanks around for me and show me the best stuff on the reef. I'm just pointing out that it isn't really for everyone.