It's just not particularly smooth and looks a bit choppy to my eyes. Perhaps it's because the character doesn't really "curl up" much.
For example, this asset has a fairly sublime looking roll animation: https://aamatniekss.itch.io/fantasy-knight-free-pixelart-animated-character
This tutorial here kind of points to what I'm getting at: https://www.patreon.com/posts/slide-roll-dash-16562907