something like 75% of video games never get played to completion, and fromsoft games, for all their popularity, score even lower than that. so most people who picked up dark souls never saw these nightmare Fleischman cartoon characters, or the sea of hopping dragon butts.
...wait, the what?
the wiki calls these things Bounding Demons, and speculates that they are the remains of the everlasting dragons that were stricken by the plague. [loredump redacted, go watch the opening cinematic on youtube if you're curious.]
my theory is much worse.
as you walk along the valley of drakes, a bottomless (OR IS IT) chasm between new londo and darkroot basin, you will inevitably disturb this sleeping beast: a decaying dragon clinging to the path with its rotten forearms, mostly because it has items you can only reach by stepping on its paws.
cursed to eternally rot and eternally regenerate, the dragon sits there, regrowing its hindquarters until they become too heavy for the rotten spine to support, and drop into lost izalith (eventually) below. so all those mindless stompy legs are the remains of the everlasting dragons, or at least, one specific everlasting dragon. grim.
alternately the bounding demons are a relic of a time recently past, before let's plays and screen sharing, when games were built with the full knowledge that 99% of players would never see the last quarter, and the final areas thus tended to be rushed. you could get away with a lava temple full of a bunch of clonestamped dragon asses and a shitty puzzle boss, and no one would ever admit it was kind of shit.
but that's not as much fun.