It's almost not about the money, even. Moving is a big deal, financially and emotionally and it takes a toll. Even worse is making the decision to move, putting a property on the market and then having to hang around for weeks or months waiting to see if it sells. Doing the work to get a quick sale will pay back in non-financial ways.
Plus, most people have no imagination, so they can't see how a property will look when done up, they just see what's there at the moment. And many buyers either won't want the hassle of getting work done, or won't know how to get the work done or what it might cost - that could particularly be the case for a condo, which will attract buyers who aren't knowledgeable or interested in maintenance work.
The other thing is: a condo doesn't have any individuality. Someone wanting to move into a condo, even a condo in a particular building, is likely to have the option of thinking "this one's a bit dated, there may be another better one on the market soon and I'll wait to see". They aren't going to think "it's this one or never, so let's go for it even if it's not really what we want".