Why did I commute? Because I lived some distance from my work.

If the question is, why did I commute by bike then the answer changed as time went on. I started because it was quicker, in Central London where I was then living, than going by public transport. I continued, even when living elsewhere, and over much longer distances, because I discovered I loved it. I liked other things about it - the fitness, the feeling of well-being, the lack of expense and hassle compared with the alternatives, but they were additional benefits rather than motives. I just loved it.