I feel like the answer to your question relates to map size, most maps don't cater to the range of scrifles, now I'm not saying that they can't be used effectively, which they can, but it is easy to see most medium-short range weapons work generally the best in most situations. Yet, when you get into combined arms it is open enough to justify the medium-long range weapons, while still containing some close quarter ish areas for those preferring their arifles, prifles and such.