my guess is its not just there for a reason!

probably engine popped, or a write-off, or stolen recovered vehicle etc
theres many possibilities its just sat there, not just that someone abandoned it.

remember 10-15 years ago some people were getting insurance quotes for £9000. so car was in a way worthless as its couldnt be used, and if it was broke then owner prob thought it wasnt worth fixing

what is supprising it that nothing has been robbed from it, as its clearly sat there for at least 5-10 years!

Also you have to remember to us its a beautiful creation, to a lot of people its just an old battered sierra.