Technical debt is debt in something non-fungible. You don't just need to pay it back, you need to pay it back with exactly the right thing. You can't just get a lump of commodity code and drop it in. That makes it much more expensive to pay back.
The skyscraper is also a flawed analogy because it doesn't cover the fact that this will somehow magically slow down the work on the rest of the building until it is fixed. The molasses metaphor is good for that one, but I don't see how I can mix the two.