Good question. Not sure why it’s like this. Perhaps wifi is ubiquitous enough that most people don’t care…? My preferred solution: I carry a small 4g router (TP-Link M7350) in my backpack. Extremely useful when working in places that lack wifi (e.g. some coffee shops etc). The battery lasts very long.
Probably a combination of (relative) WiFi ubiquity, the ability to use a phone as a hotspot in many cases, and as soon as you're using cellular on a different device you're talking about a subscription of some sort. I don't use cellular other than on my phone enough to even activate cellular on a couple of other devices of mine that have a cellular modem.