Like what? Redevelopment takes a lot of planning. For any building of that age there'll be a considerable sized asbestos removal job - it'd be costed in to any development plan. I think it's taken this long because nobody has been able to decide what to do with it.
They'll have to remove the asbestos before they do anything with it (whether it' demolition or conversion). So you've got that cost up front to deal with.
And all the contamination from former medical equipment and around the boilers. And, not to mention, the claims that there are bodies buried around the site.
All the best,
Simon