Part of that is because of increasing regulation on landlords and buildings. For example, just a couple of weeks ago I roughed in new electric for a two bedroom apartment originally built in the late 60's or early 70's. I had to remove old asbestos sheathed cable used to wire it originally, along with some aluminum wiring installed at some point in an upgrade. That came to $2500 and I was charging easily half price on what guys trying to make a full time living off doing that sort of thing would charge. I still have to do the finish when the drywallers and painters are done. That'll be another $1000.
That doesn't include the cost of new insulation, drywall, paint, flooring, and whatever that one apartment is getting. I can easily predict it'll cost in excess of $20,000 to upgrade that one apartment in a 20 unit complex to bring it close to current code compliance. Yet, we have idiots like AOC and Joke telling us they're going to rehab hundreds of thousands of buildings to make them "energy efficient." They are totally full of shit.
Of course, the owner of that complex is going to charge more for rent on that upgraded apartment too...