Motorised bicycles and licences

I would like to respectfully ask a couple of questions to the ADT. How come a 50cc motorbike (moped) manufactured by a reputable company and imported through normal legal channels needs to be registered and insured, and can only be driven by a person over 18 years of age who holds a valid driving licence, whilst a bicycle that has a similar sized engine most probably fitted in Malta by an unknown person and certainly has not been tested and certified can be ridden by anyone, apparently no matter what his age may be, without any licence or insurance? I would like to know what the repercussions would be in the event of an accident involving one of these bicycles.

Also, according to the ADT adverts in the local media, any imported vehicle must be registered within 15 days. How come a foreigner who is living on the islands for the past six months can keep a foreign registered car and scooter on the road with foreign plates? This, to me, is discrimination against Maltese people.

From previous letters that I have followed in the newspaper, it seems that it is not part of ADT's policy to answer questions because a lot has been written on various subjects and hardly any replies have been forthcoming. I sincerely hope my simple request does not fall on deaf ears.