I think for me with the diving that I do it's unnecessary and inconvenient. I'm young and strong enough to back mount my tanks, I have muscle memory for where slung bottles and isolator valves are, I have no physical ailments that prevent me from lifting a full technical kit or reaching valves and I'm not squeezing into the kind of tight spaces that would necessitate the use of a different configuration. I'm not opposed to it if the dive calls for its use, or if you've got a malady that is relieved by side mounting. But for young, strong divers doing mostly open water stuff, I just see backmount as the better tool.
Someday, I might change my mind on that... for now, I'm happy where I'm at.
Someday, I might change my mind on that... for now, I'm happy where I'm at.