The stadium was allowed (in fact, actively encouraged) to go to rot after about 1986-87, when then-owner Tom Monaghan decided he wanted the taxpayers to build him a new stadium. In order to get this done, being able to cite the ever-more-decrepit condition of Tiger Stadium was necessary.
Mike Ilitch continued this strategy after buying the team and finally succeeded in 1999-2000. After Comerica Park was built, Ilitch's company, Olympia Entertainment, received a yearly sum of $400,000 of city money for "security and maintenance" on Tiger Stadium, presumably to keep it in somewhat-usable condition for renovation projects. This $400,000 came out of a fund of $2 million, which was exhausted at the end of 2005.
The "security and maintenance" efforts mainly consisted of putting padlocks on the doors, walking away, and cashing the $400,000 checks every year. The physical condition of the stadium is simply rotting away. Vandals quickly busted past the padlocks and have stolen/destroyed virtually every single item in the stadium which might have been useful as memorabilia. The fabric-covered "Tiger Den" seats (with Olde English 'D' symbols) have all been chopped to pieces by vandals.
There is nothing left of the stadium now. It needs to be nuked tomorrow morning. The City of Detroit, mismanaged by an incompetent corrupt thug mayor in Kwame Kilpatrick, has barely enough money to turn on the lights at city hall. I suppose if the city agrees to pay Ilitch $2 million more, he'll be happy to have it done.