Werebears are in lore. They were supposed to be a really big issue in Skyrim. That's why everyone was suprised not to see them in vanilla Skyrim, and even more so when Dawnguard came out, especially after seeing they had already made one for the Gamejam.
Werebears are stated to be the most common lycanthrope, yes, but the author of said book
never encounters one or nor any evidence to suggest they actually suggest. Now werewolves on the other hand... two of them in his search for werebears.