I’m sure you’ve heard the old saying, “They don’t build them like they used to.” People apply it to everything from cars to hamburgers. “They just don’t make a cheeseburger like they used to.”
Perhaps they don’t.

I recently removed a dozen wood doors from a building and replaced them with steel doors. The building is receiving a massive renovation and the new doors are all steel. Now, they don’t build wood doors the way they used to. Most new wood doors I put on in commercial buildings are made out of particle board with a thin wood veneer covering the whole thing. The edges have around a quarter inch of solid wood. The veneer is actually first glued to a thin layer of MDF which is then glued to the particle board. If anything hits the edge of such a door, the veneer starts to peel away.
It wasn’t long ago that such doors always had a thin layer of plywood one each side. the veneer was thicker. The edges had almost an inch of wood.
I was talking to someone who was looking at the hole for the lock in the old door I had removed. He asked if the door was solid wood. I said, no, it’s made of particle board but where the lock goes, they had a block of solid wood. Of course, there is no such block of solid wood in such a door, anymore, because they don’t make them like they used to.
It’s just an example, really, to illustrate a trend in manufacturing. Years ago, someone decided to mass-produce wood doors. Those doors had to be as good or better than doors knocked together by hand. So someone had to think about what was needed to make those doors good and designed them accordingly. Doors need solid wood for mounting in the frame. They need impact-resistant edges. They need solid blocking for hardware.

Over time, someone in charge of making the doors more efficiently decided that none of that stuff is needed. I think it’s mostly someone just looking at all the work being done and saying, “Why are we bothering to do all that? If we reduce the amount of actual wood in the door, it will still look the same and that’s all that matters.”
In manufacturing, efficiency equals lower cost and shorter time to make.
In short, they don’t make them like they used to because they forgot or never knew or don’t care why they were made that way at all.

The doors I removed recently were around 50 years old. The wood was scratched and dented, but nowhere was the veneer peeling. The hinges were all firmly attached to every door, also. When I put up new wood doors, I drill holes for the screws and the edge still splits because there is nothing there with any strength. Who needs something like that on the edge of a door? It looks the same if it has a piece of wood-grain Formica glued on some cardboard. Fill the inside with vermiculite and it’s really fire-resistant. It’ll last so long as no one actually touches it.

I admit, this is a personal peeve because I do install a lot of such doors. And since it’s my actual work, for which I get paid, I’d appreciate it if the work I did could last for at least a few years without being undone by the inferior construction of the things I’m installing. But all that aside, there is something significant here that applies to everything. Economy undoes a lot of intelligence in design. Penny-pinching will first remove all the structural elements that cannot be easily seen or understood by the penny-pinchers.

By way of contrast, I once needed to replace an old steel door on a building that was being renovated. I was surprised when I lifted it to find that it weighed very little. It also was not at all rigid. It was actually very thin galvanized sheet metal wrapped around what appeared to be tentest but was likely some asbestos-based fibreboard. It looked like it may have been made by whoever put it up, but I think it was actually a manufactured product. It was good, because if you happened to forget your key, you could get in by cutting a hole in the door with a pocket knife (one with a can-opening attachment). They don’t make them like that, anymore.