I hate arguing about this because it makes all the characters look like video game characters (how everyone has to have a power level and health bar).
But anyway, yeah, some of the more recent riders seem like they CANT STOP USING THEIR ULTIMATE FORM. It's getting old... REAL old.
As for Kabuto, I am pretty sure their Clock Ups are only available for a limited time. Besides, the Worms also had Clock Ups, which, would make a lot more sense for the Riders to have them too.