They won't uncap it mostly because trying to balance every fight around a BLU's 120+ spells would be a pain. Also, it was designed for solo content of Carnival in mind, not soloing primals. The only thing that made people think BLU could solo primals was the trailer that showed BLU soloing Shiva and learning Glass Dance, but this was a showcase. They also showed off SB BLM spells with BLM soloing Susano and they later showed BLM soloing Chaos. They're trailers/showcases not to be taken literally.