I think it is mostly because they don't understand how much better wired internet is than wireless. I've basically forced many people to connect their devices with Ethernet as a "temporary" measure to solve their problems. For the most part, every single person has decided to leave whatever it is connected. Almost all my friends rent too, which is a huge barrier to using wires, since the wires can't be hidden in the walls or ceilings.

One of the big things that people don't realize is that bandwidth of wireless is split between every device on that channel. So if you are streaming to your TV/roku/xbox/etc over wifi, you are killing the bandwidth for your laptop and phone as well. Plus, if you live in a city your wireless bandwidth is pretty much guaranteed to suck because every ISP includes wifi with their modems, destroying the noise floor. Comcast modems are a particularly notable example, as they have a "public" 2.4 ghz network in addition to the "private" 2.5 and 5 ghz networks. There are no fewer than 30 wifi networks available inside my house when I check on my phone, and I live in a row house with metal lathe under the plaster, which greatly attenuates wifi signals.

I think the biggest barrier to wiring things is that patch cables are incredibly expensive if you buy them at Best Buy, etc. Most non-technical people I know only own the patch cable that came with their modem. Once I get them wired up, they are astounded by how much faster their internet is. They don't have buffering issues, the internet doesn't drop randomly, and it just seems "faster" (which I attribute to lower latency). I toss extra patch cables in my Monoprice orders now and sell them to my friends at-cost. To be honest, it's partially for my own sanity as well, because watching Netflix at 480p on a 50/15 connection drives me nuts.