Most sling attachment points have been on the bottom because throughout history it simply wasn't feasible to hang a LONG gun (remember, up til WW1, infantry rifles had 30 inch barrels, and even in WW2, 25 inch was normal) in the manner now common. With the rise of submachine guns, assault rifles and everything in general being shorter, it is. Bottom sling swivels are for administrative carry, like road marches (75% of the job of the infantry prior to WW2) where no combat is expected.
Nowadays, having a rifle permanently slung "ready" is more likely and common. Post 2000 it's a lot more odd to see guys with rifles slung over a shoulder on their back, unless doing an admin movement, or mountaineering, etc. For hunting rifles, the bottom sling mount is still normal, but you see more guys modifying bolt guns, etc for side sling mounts due to experience and preference. For a hunting gun, the bottom mounts don't bother me, and some hunters even remove a sling completely so it won't tangle in brush when hunting dangerous game. But for .mil guys and those of similar experiences, a modern 2 pt quick adjust sling, even on a hunting gun, tends to be preferred.
My work rifles are all set up that with with a VTAC or similar. My hunting rifle, being a century old Mauser, is not......
But the next one (modern) most likely will be, since it will also be shorter/handier (20-22" barrel).
My work rifle is always slung ready at the front, excepting one time when performing CPR (too late) on a murder victim, where I slung it on my back. In that case I had 2 others with me and we all had pistols as well readily accessible.