Might be although I don't know. I've had my share of stoplights and I never kick it into neutral unless there's a train or I'm stopped for construction and then I shut the engine off. Clutch cable is still in good shape too.

I don't think frequency of use has anything to do with the spring getting weak. It seems to me that it might not have been as strong as it should have been in the first place. Springs are made to be cycled like the valve springs for example.

There's a big difference between the release bearings for your car and your bike. The car bearing is packed with a finite supply of grease while the bike bearing is flooded with a constant supply of cooling oil. Grease can be described as a sponge that holds oil and after the oil evaporates or otherwise dries up there's nothing left but a dry lump.

The placement of the motorcycle clutch puts a lot of strain on it. Take the engine crankshaft torque and multiply it times the primary drive ratio and you'll get the torque the motorcycle clutch has to endure.