I can't speak to the motivations of others, but I can speak to mine. My reason for listing my camera and lens is merely to list out the tools I use, so when I post an image here at POTN viewers can see the toolset I used to capture the image. And I started doing it because I appreciated that others did it as well (whatever their motivations might be). It can be a bit more convenient than chasing down the Exif data.
I don't expect you to understand or appreciate those motivations, but try to be more tolerant and not as disparaging toward those who may have different interests than you do. Rest assured that you can put whatever you like in your own sig...I won't be starting a thread finding fault with it.
So, besides gear lists in the sig, what else don't you like about POTN members? Welcome.....I guess.