With bullet weights typically used for Deer & Elk - 150 Gr to 180 Gr,. the 7mms have a better BC, for better velocity, less drop, and greater energy beyond 300+ yards. I used a .284 Win. for years before trying a 7 Mag, but ended up with a .300 WSM, which performed great on an Oryx at over 450 yards. I think this one of the short mags will be around the longest, although the 7WSM is perty good!!
Also, knowing how "frugal" many New Mexicans are, the ammunition for 7mm Rem Mag is frequently priced on par with .270, .308, and .30-'06, when using "standard" bullets. Add to that that the 7mm Mag has the magic "MAGNUM" attached to its name, meaning to some less well-informed "hunters" that "if you hit it, you'll kill it" adds a little sales psychology to the mix.