It's tough to convert office space to housing. Thing about a floor of cubicles: how does that become 10 apartments each with a kitchen, adequate windows, and bathrooms?
You can get a bit creative with this too: e.g. dedicate some floors of the new apartment skyscraper as co-working spaces, and try to plan it so that everyone who rents in the building can use the co-working spaces for "free" as part of their rent and still have some leftover capacity to sell co-working memberships to others nearby as well.
There was some reasons for leaving it in place, and to be fair a major renovation would have to run into these hurdles either way. But it's probably going to be quite a bit more costly then you're imagining.