A possibility:
Kedusha is impossible without Tumah (before Moshiach), and as Kedusha grows, Tumah must grow as well (Similar to Newton’s Third law). In order to have a “Koach Kedusha” i.e. Moshe Rabbainu, there was a requirement to have someone with the “Koach HaTumah” equal to Moshe.
Not my style (too Kabbalistic), but its an idea.