Asking what anyone takes away from any sort of music you don't have a personal interest in is an exercise in futility. Because music is about emotional connections, which are completely subjective, you literally can't understand it if you don't understand it.
That aside, I will try to explain my experience.
First, the extreme forms of metal (death, grindcore, technical death, black metal, progressive death, metalcore, deathcore, etc) are what the name implies. Extreme and dark. Some people like these things. Why do people like slasher movies, rollercoasters, drag racing, MMA fighting, or structural demolition? It is visceral, and kinda fun.
These extremes in music are a swirling mass of frenzied chaos that is only held together by the sheer will and playing skill of the people writing it. It is a beautiful blend of animal emotional and intellectual brilliance. It is the raw human id raging against the lame vernier we place on civilization, acting out in a skilled way that requires the most human of learning.
The bass playing is only one part of the music. You can't separate any of it into pieces and isolate it. It is all context. The bass playing is fast and aggressive because it needs to be. The guitars are super saturated because they need to be. The lyrics are bizarre or grotesque because what else could they be with that musical background? The vocals are harsh and guttural, because anything else is too weak to give the words meaning or mix well with the music.
There are thousands of bands like this with millions of fans world wide because, in its own way, it is beautiful.
To tie this back to the OP, the names are what they are to help consumers quickly ID the band. All genres do it. It is a tradition that goes back to Black Sabbath, the first real metal band. They took the name from a B horror movie. Like so many other things they did, it set the standard. If Death had called themselves The Chuck Schuldiner Five, no one would have listened because it is a corny name that makes people think of old and dull music. If Cannibal Corpse had called themselves something like Buffalo Tampa Connection, they would have gone nowhere. If Dying Fetus had named themselves Gross Stuff That Actually Happens, same thing. If any black metal band just called themselves It Is So Damn Cold and Dark in Norway, it wouldn't have the same appeal.
Bottom line: The names are marketing, don't think to hard about it. The lyrics are either the writer seeing how far they can go, things they are mad about, homages to books or movies they like, or are telling fantasy\Sci Fi stories. Vocals are what they are because singing like Frank Sinatra to the music would be incredibly stupid. And the music is fast because the people playing it, and the people listening to it, think it is fun.
