I've never owned a car - I've often thought it would be convenient (funnily mostly in terms of getting to cycling events - TT's, races, sportives etc.) but if needs be I can usually use public transport or get a lift.
As for why cycle? I've often wondered this. Recently I thought about all the reasons - it's cheaper than a car (sort of), it keeps me fit, saves on gym membership, gets me outdoors and breathing fresh(ish) air. And then, cycling into work in the freezing cold p1ssing rain one morning I thought, 'The real reason I cycle is simple: I just love riding a bike.'