is that it's unnecessary to burden cyclists with a mass of legislation relating to their use of the roads.
They (the cyclists) are considered to be vulnerable road users, in that the threat posed to others b a cyclist is far less than that posed by someone driving a ton or so of metal at 30 mph. It's considered that a motorist has a duty to look out for cyclists, although cyclists must obviously obey road-traffic laws. Lots of cyclists tend to be quite young, and legislators are aware of the problems associated with requiring youngsters to comply with all kinds of rules and regulations. For instance, it's the law that all new bikes must be fitted with a bell at the point of sale, but there's no legal requirement for it to remain on the bike, once it's on the road - you may legally remove it.
It's a legal requirement for motorists to avoid driving in special cycle lanes, and you can be prosecuted if you do it. Cyclists, on the other hand, are not legally required to ride in the lanes, even if they're there - they can ignore them if they like.
I take your point about the safety aspects of rear-view mirrors, and it could be said that if a rear-view mirror is a legal requirement on a motorcycle (and it is) it should also be fitted to a pedal-bike.