For what purpose it’s sent in the space???
The first launch of such a complex rocket was highly likely to end in an earth-shattering kaboom, a shower of scrap metal (and a load of invaluable information as to what went wrong). Even by spaceflight standards, it would be too risky to launch anything "worthwhile" which would have cost a small fortune to build. Plus, there's the PR angle: even if you give a free launch to some enthusiast/charity/university project, there's no
good way to spin it if it gets blown up.
However they needed something in the nose to simulate the weight of an actual satellite/spacecraft - and you have to admit that a sports car with a dummy astronaut, "Life on Mars" playing (if inaudibly) on the stereo and a copy of the Hitchhiker's Guide... has more style than a concrete block. (Elon loses marks for forgetting the teapot, though).
...and, y'know, when the aliens finally stumble across the cinders of our solar system, what would you prefer them to find? A dull and worthy gold record containing some committee's idea of a sanitised representation of our diverse cultures - or a dummy in a sports car, and one of the books best-suited to convey the message "Hey, some of us actually realised how hilariously stupid our race was?"