1) He`s really broken and cant pray (unlikly)
2) It`s not enough for him to pray, lunarians should stop being scumbags, they fail
3) Praying is not a mere technical issue, Sensei must wish them to achieve peace with his heart, but he cant because they are scumbags and insulted him for many centuries.
4) He doesn`t want to, for the same reason.
5) Praying doesn`t just remove lunarinas, it has another meaning, like restoring humanity for example, or it has another sequences which we don`t know about. I would bet on this one.