A registry style ceremony is a quick, legals only ceremony with maximum 10 people. It is over in about 2 minutes, as it only contains the mandatory legal requirements. Basically the same service you'd expect if you went to a registry office. No bells and whistles - it's all about getting that piece of paper. A registry style ceremony is generally a much cheaper option, as there is less work involved for a celebrant.
A 'normal' ceremony requires much more love and attention. As a celebrant, there is much more involved including writing a personalised ceremony with you in the months leading up to the wedding, and then organising everything on the day including setting up a PA/audio equipment so the ceremony is audible, liaising with suppliers like venue managers, photographers, videographers, guests, and the bridal party. The celebrant then holds space for the ceremony including welcoming everyone, telling your story, coordinating the music, supporting the couple through the vows/rings, signing the paperwork, wrapping up the ceremony and setting the tone for the rest of the day!