User blog comment:B214/Question and Answers 6/@comment-2601:87:8300:20D0:F9A4:9909:2C16:6991-20190610123610/@comment-33359929-20190610152125

It's actually stated that Vasco was approached by Uriel and Raphael and had an offer to become a Reincarnated Angel, but Vasco refused, saying he wanted to die as a human.

We don't know his reasoning beyond that.