"That meteorite fell out of the sky, it belongs to all of us."

If it "belongs to all of us" means no one owns it.
But if offered for sale then it does actually belong to all of us- anyone can choose to exchange some paper for it. Or decide not to buy it.
It's not as though universities or museums are poor. It's not as though public schools don't have a enough of money to buy this sort of thing- assuming they want it.
And you are free to buy some and show it to or give as many people as you like. Take it out of the alcohol budget.
Or take it out of travel expense, it would require for you to go get some.

A high price, ensures that people will go out onto a frozen lake and recover it before the lake ice melts and it sinks to the bottom of the lake. They also take care in recovering it properly.
Besides, if the rock falls and hits your car or go through your roof- you could make money out of the deal.