Board Thread:Show-Related Questions and Answers/@comment-25491743-20150817210639/@comment-25926288-20151226214602

Rumple was trapped in there, so it can hold powerful beings. So, they just didnt think to use it.

The hat wasn't made to trap powerful magic users. It does that, but it was made (speculation) to cleave the power or Darkness from the individual. Why else would the Apprentice who was around the hat for centuries use it for that specific reason.