Because the footprint is so expensive, you don't have the cash to invest in quality without making the building too expensive for the people who are going to be using it.
And the footprint isn't the only thing that's more expensive, all the cool new technologies that your grandparent comment brought up are all more expensive to implement than structures without them. The existence of those technologies implies the existence of skilled professionals to plan and install them. It used to be that you just needed to pay your architect and engineer and builders, now you gotta also pay your crane operators and electricians and plumbers and acoustic consultants, and fire protection experts, and geologists, and network engineers, and energy consultants, and accessibility consultants too and they all want to be paid well for their expertise.
The proliferation of skilled professionals reduces the appetite in the population in general for unskilled manual labor, so that gets more scarce and expensive too. Gotta pay the builders well or else they'll quit and change careers to be one of those professional types.
Add to that the regulatory and compliance requirements that raises the floor of acceptable quality (building MUST be energy efficient, accessible, fire-safe, earthquake-safe, minimally ecologically impactful, etc etc etc) and your wiggle room for where to focus your "quality" budget is pretty tiny and exterior aesthetics rapidly sinks to the bottom of that list.
[disclaimer: I actually disagree with the people who say that new buildings are ugly. I actually like the modernist and international style aesthetics that are artistic declarations of raw functionality. My town has a brutalist city hall where the council chamber juts out in an overhang, so when you walk by you can look at it and say "that funky structural appendix is the exact room where people are making important decisions at this very moment" which I think is cool. This post-modern concert hall just opened a few blocks from me and I think it's pretty sexy: https://wysomusic.org/wp-content/uploads/Screen-Shot-2021-11... ]
