We've noticed the same thing round here - very few people actually use their garages for their cars - I think I can see one person who does, from my front window. However, since the houses all have off-road parking too, it isn't really a problem.
As others have said, garages seem to accumulate junk - ours certainly did, after we moved in, even though we knew that we were going to convert both of them as soon as we could get permission. A number of people have converted their garages too - we've certainly found them to be far more useful as rooms than they ever were as garages.
We did once put one of the cars into the garage - when we were away on holiday the first year we lived here. One car went in longterm parking at the airport, and the other in the garage, but it was the tightest of tight squeezes, with literally an inch either end of the car, and only just enough space for dh to open the door and get out.
I suspect that developers aren't particularly generous with the size of their garages, and cars have got bigger and bigger over recent years - and these two factors have combined to make it very difficult to use a garage. Plus, as dh has told me, car paint technology has improved a lot, so there's no longer a great need to keep your car out of the weather to keep the paint from fading and ageing.