Demonic cultivators were an oddity amongst oddities. There were many of them due to how easily it was to sell your own soul to a demon, at least it was much more easy than to actually cultivate. Having to painstakingly reach the realms, meditate for entire days, absorb unholy amounts of strange substances to boost yourself up.
There was a reason as to why this continent never saw that many overpowered cultivators, cultivation wasn't for the first random guy on the street. Even reaching the mortal realm was hard and it was only the second realm.