"That's just how spirits are," Alley shrugs, "but he's changing now that he's halfway like us mortals."

Spirits who are fully spirits really don't operate like whole people. They embody their concept, and that's it. Change is dangerous, lest a spirit twist into a demon.

Cole was really quite a special case. Or perhaps Compassion was always easier to change, due to its nature... and rarity, meaning even Solas couldn't have known for sure.