I'm guessing the main reason the optics are so large is for the F2.8? Man...buying lens filters must be like buying a windshield for a car. They can't be cheap at that size!
As Lunar was saying, practically every one of these sort of telephoto lenses (as well as ultra-wides and fisheyes) use internal or rear-element filters. Such filters are quite small, actually.
Large, expensive telephotos will likely come with a decent moulded case, but you still need to get an ATA-rated case if you are going to travel on an airline.
As for large front optics, this Sigma lens is not the craziest telephoto lens I've ever seen. The craziest looking telephoto lens ever is the hyper-rare Nikkor (Nikon) 400mm f/2.0. There are 400mm f/2.8 Nikkor lenses around (and quite expensive), but only (I believe) 7 of these 400mm f/2.0 lenses. The front element on the Nikkor 400mm f/2.0 telephoto is about
50% larger than that Sigma lens pictured above. The body of the Nikkor 400mm f/2.0, though, is about half the length of that Sigma lens.
I read that Nikon sold far more of the very exotic 6mm fisheye lenses (several dozen) than the huge and reportedly heavy-as-hell 400mm f/2.8. By the way, the Nikkor 6mm fisheye's field of view was
more than 180 degrees -- meaning you could see everything in front of you as well as some of what was behind you!