Keep in mind a lot of the homes around here are old. Mine is almost 130. None of the dimensions match modern dimensions. You can't just swap out a door. You either have to have it custom made, make your own, or rebuild the doorway. The walls and ceilings are plaster not plasterboard. Well, the original layer is plaster. Plaster is messy to deal with. Easier to DIY if you're working alone (no lifting heavy boards), but still messy and more time consuming (3-4 coats vs 1-2). There might be one to three more wall/ceiling/flooring layers on top of that. Are you going to add a 4th or redo it all properly? Everything will have lead paint on it, even my bedroom floors have it (I added another flooring layer). Dealing with that properly takes $$$$ if you hire someone or just $$ plus a lot more time to DIY it. Oh, and the certified lead test swabs you're supposed to use have been out of stock since the pandemic. Sure lots of people sell them online, but you order from them and they just cancel your order. Had that happen 4 times.

Also with homes that old, there's a bunch of people who want to preserve the look. My stair banisters are really fancy. Things like that disappear when you remodel.

Old carpet? Who the fuck cares (especially when I don't have enough outlets and can't find a reliable contractor. Now I've got to find a good carpet guy too? Why didn't my college have a Handyman degree). I don't spend any time with my face buried in the carpet (okay, I'll admit to doing a few pushups now and again). If it still works then it still works. Plus I don't trust newer things as much. They all seem to wear out faster. Even older building material was more durable than modern building material. If I replace it now then I'll have to replace it again within 10 years. Why not put it off a longer.

Finally, I can't keep up with renovations when there's so many questions to answer on Reddit. They just keep coming in faster than I can reply.