I'd say the reason that 175's are not so popular is the large proportion of people who base their choices on ballistics charts, not performance IN game. That. and the fact that by far the biggest proportion of game animals shot with the 7mm mag are deer or deer sized game.
I'd pick the 175 grain over lighter bullets every time if hunting Elk, Moose, Woodland/Mountian caribou, Bison or Bears. And on a mixed bag hunt heavier is not a handicap for the small stuff.
But most north american hunters shoot deer and maybe pronghorn or sheep and such, so the heavy bullets are not needed, don't look as good in the long distance "drop charts" and so are not popular.
