Why are cars updated yearly?

It seems kind of stupid to release a different version every year instead of making a model once, say every five years. I can understand why in electronics there's a new model every year: because Moore's law, the stuff is getting better so much faster. But when cars of today look, feel, and perform the same as they did 5 years ago...why fragment the market? Is it just greed? Too many people profit off of this 1950s business model of different proprietary parts and maintenance? The expected life of a car nowadays is 10 years/150k miles and yet they release an update on a yearly basis for the thousands of different models on the road like we're going to throw our "old" car away right after a new one comes out.

Can someone explain this to me?