It is an alternate to paying the full fine. If it is too long it will increase likelihood for scofflaws to pay the ~$200 fine instead of $50 and 2hrs of their time (which is more likely 3hrs with travel time) Also a longer class will cost more so it could for example be a $100 for a 4hr class which would be even less desirable than $200 (at least for those that can afford it)

Motor vehicle classes can get away with longer classes as the motivation is for drivers to not get points and increases in insurance.

More important than how long is the content. Is it 1hr of lecture on needing to wear a helmet plus how to check brakes and tires.