User blog comment:IamJakuhoRaikoben/Chapter 361: The Two Bombs, Review./@comment-5668006-20131123040415/@comment-1359322-20131123104434

From what the eggshell demon said, maybe the number of times they can use the curse is limited or maybe it has some limitation like Tempesta loses his body when using his, so they learn magic to compensate only using their curse when cornered.