Larian has granted access to multiple forms that break the CR cap or the movement type limitations:
https://roll20.net/compendium/dnd5e/Druid and look at the limitations under Wild Shape.
Even Circle of the Moon should only be able to get CR 1 at 2nd level and druid level divided by 3, rounded down, at level 6 and higher. Polar bears are CR 2 - shouldn't be available at all. Flying forms shouldn't be available until level 8.
Basically, it means they wanted people to have a lot of shapes available to make it flashy, but then had to nerf the actual shapes to keep something that looks like balance.
