usually when they do something like that it's either kids, who go for a joy ride and then burn it.. or someone uses it for a crime of some sort, and burns it thinking they covered all their tracks up.
I see a lot of nice vehicles that get torched, when all they wanted was the seats or something. It just seems to be the trend these days.. I guess they think any evidence, that could lead it back to them, burns up too.
I've seen many a person, late at night, show up not knowing their car was even gone, until they got the call from PD saying it was stolen, and torched.