Where traditional gi BJJ can be slow and methodical, no-gi tends to be faster and more explosive.
No gi BJJ is when both players wear rashguards and boardshorts, which they cannot grab during a match.
It's extremely difficult to hold someone down without all that extra gi material. Things are slippery, you don't have gi grips, there are a ton more scrambles, and it's harder to get submissions.
All this makes No gi more entertaining to watch and compete in.