The most fiddly items in my camera gear are the filters. Those are pretty much the only things I keep dropping while trying to screw then (except for my remote trigger falling once into a river, next time I'll buy the waterproof one).
Lenses used to be screw mount and now use a bayonet. Lens hoods used to screw on and now they use a bayonet. So, why do filters still have to be screwed? Bayonets are so much easier!
Obviously this only applies to round filters but square ones with a holder are really unwieldy for other reasons and quite bulky.