Probably because look at the demon lord
!!!MAJOR!!! Spoiler.... DO NOT READ IF YOU DON'T WANNA BE SPOILED!
So kumuko will one day have a human form (on the volume 7 of the ln), she will technically become a god because she transcended the system(she isn't a part of it anymore). If you watched the anime, you would actually see "Shiraori" aka Kumuko's human form. She's the one who always has her eyes closed, has white hair and skin, and btw she's the one who killed Julius. And.... because she was once a spider, she can still switch to that form freely without the system's help.
Wait so she’s on the other side ?
I thought she would be with her friends （/TДT)/
Again spoiler...
Nope, she's just a god but she's not dead, she's always mostly by Ariel's side when she appeared on the anime btw if u didn't notice . gods in that world are all immortal unless you destroy their soul. Her true form since she trancended is her soul, her body is just a mortal vessel.
Hmm will she keep evolving? Like will her evolution ever reach a point where her physical form is completely human or she can at least morph into one so she can roam in the surface without being suspected or whatever?