Not to challenge your comment, but we have been converting office high-rises into apartments all over Detroit seemingly quite successfully and tastefully - with buildings built in the 1920s no less.
It is hard to generalize, but I would be willing to bet that it is cheaper to convert more modern, recently built or still under-construction office high-rises.
I am living in a converted office high-rise (built in 1914) right now in fact: https://en.m.wikipedia.org/wiki/Kales_Building
And there is another in the middle of conversion right next door: https://en.m.wikipedia.org/wiki/United_Artists_Theatre_Build...
It is hard to generalize, but I would be willing to bet that it is cheaper to convert more modern, recently built or still under-construction office high-rises.