I am not advocating using your quad in wet conditions.
If one of my quads were to get wet I would blow them dry with compressed air. My crawler motors get wet as does my short course truck frequently with no issues.
Even the electrical components are water proof on them so crossing a small stream or ditch does no harm.
For years hobbies have been breaking in '
brushed' motors in water. Brushless, like used on quads do not require this.
The bearings are typically sealed and if it is fresh water (not salt), it is pretty harmless for the motor itself.
Here are a couple of brushless motors in water...