Re: "Why you put an engine on your bicycle?" and best answer goes to...
I'm generally not enjoying the direction of social and governmental evolution...the 'Man' wants in my wallet, in my house, in my car, in my LIFE! Every time the big guys get together in DC and state capitol, more things are illegal, regulated, and taxed! A motorized bike is, for now, a great symbol of beating - or at least avoiding - the 'System'! Cheap, no registration, no insurance, I can hide it in my backyard...totally under the 'Man's' radar (at least for now).
...or maybe just because I like to tinker?
Thomas Jefferson and Ben Franklin would have LOVED motored bikes!