Board Thread:General Discussion/@comment-26006155-20190617222636/@comment-32182236-20190621114051

As for meta-reasons for why Toby Fox created the rule:“It would take ALMOST ALL of the monster SOULs in the Underground to equal the power of a single human SOUL.”

...This was to make Asriel Dreemurr's fight plausible. Remember, it ends with him using six SOULs, plus almost all the monster souls (Napstablook didn't make it), to break the barrier.

However, the glyphs were made before Chara even fell, as I proved earlier, so the numbers could have changed afterwards. This is one of the cases where Toby made it more obvious than it could have been-Probably because he wants us to understand the ending before we learn about what happened to Gaster.. Though if Toby DID make it "more than all monsters in the entire underground", and gave us Asriel, that would directly hint at/prove that the monster population grew... But Asriel wouldn't have known that there were enough now, so the fight still breaks.