It's not about "using it", it's about transporting as you see fit. A good-quality rifle can easily cost $3000, and is a device of precision mechanisms & optics - not something you want strangers throwing about for hours a la "checked-in luggage", especially as if you're transporting it you will need it in good working order upon arrival (likely the point of the trip). Sure it's long, but a slim-fit case can go into the coat rack well; "takedown" models in-case would fit well in the overhead bin.

Yes, I have travelled with one. Check-in etc was more a hassle, and no more "safe" for all concerned, than if I'd just carried it on.

Some smaller flights make the issue laughable: for all the trouble of checking in luggage, screening it, and securing it for the trip, it's all ultimately just stowed behind a curtain in the cabin.