Back in 2016 or so you could get a RaspberryPi 3 for $35. Add a $5 power supply, $5 SD card and $10 case (or 3d print your own) and you've got a nice little piece of hardware for running a tiny project at home for ~$50. More than enough for hosting some simple web services, backup software or something like Home Assistant.
Plus it was popular (which makes it even more popular). It's always been very easy to find guides written specifically for the hardware, despite it's limitations.
I think the value proposition has been dropping steadily though. They cost more, are hard to find and there are now a lot more competing SBCs on the market. RaspberryPi still has name recognition though, for now.
"Rachel Powell, a woman who rawdogged her husband multiple times for the purpose of procreation, was found guilty today." doesn't have the same ring to it.