Geralt does not roll to dodge blows. He knows how to flip.
No one expects it.
Because why would someone who is 200+ pounds in armor be in the air, effortlessly evading everything? (This video is great. Geralt wouldn’t be doing this level of complicated tumbling, but just watch how cool it is). Rolling is impractical because his swords are in the way, the ground may be uneven, but most important of all is: the last place a witcher wants to be is on the ground where he has limited movement.
It can be dangerous on rocky or slippery ground so Geralt pays attention to his footing and his surroundings. (Also, if he’s recovering from a leg injury he limits his flips as much as possible).
It’s a hell of an intimidation tactic.