Because that is what people are prepared to pay for them, plus a large dose of brand snobbery. It's perfectly possible to buy a low mileage sports car that will do double the speed limit for 5k or a small runabout for 2k, I have done both.
Mazda 5 should be cheap, we borrowed one once and my partner sat comfortably in the middle (my son wants her next to him at all times when in a car). Grand Picasso was the best for interior / practicality though, by far, I'd rent that again if needed.
Why are cars so expensive?