But I guess most people don't transfer files in their local networks anymore and use their network purely for internet access.
I think this is clearly the case. Most new laptops don't even bother with a wired network port. I've got a new "pro" HP laptop the other day, and it only comes with some cheap Wi-Fi card. And it's not an "entry-level" laptop, and it's thick enough for an RJ-45 plug to physically fit.
I also see more and more desktop motherboards come with integrated Wi-Fi. The desktops at Work (HP) also have had integrated Wi-Fi for a while, and it's not something we look for (they all use wired Ethernet).
Some people just don't care.
I'm busy retrofitting Ethernet in my house by pulling cat6 through the walls and pulling out the old cat3 phone cabling. It's much harder work doing two cables (not least because none of the phone cables were in conduit, so it just starts off harder already) for each pair of ports, but it's very much worth the effort.
They didn't care, they just laid some sort of cable because that's all they had to.
there are a variety of ways to screw that up. i've seen a house that has a bunch of cat 5e run, but the installer stapled it down, and most of the cables have a staple through them somewhere along the run, killing a pair or two.
Cat6a is probably the sweet spot for home/office/etc structural cabling. It's not much more expensive than Cat6 (or Cat5e in case people are still putting that up), and has more than enough legroom.
If each run is <55m then Cat6 can still do 10Gbps.
Most people don’t have anywhere in their local network to transfer things to. I still laugh when people see my home server and assume that’s “your work thing”. I do use it for work, but 99.99% of what’s contained in there are family pictures and photos.