It works out of the box, is very easy to source (hell some brick & mortar stores sell them), has very good Linux support due to its popularity, and makes up a large part of the install base meaning HA support for it is unlikely to get deprecated.
Thus the Linux/RaspberryPi underlying complexity is irrelevant to the user - the "complexity" is to dd/BalenaEtcher/etc a downloaded file to an SD card, put the card in the Pi and connect it to power. From there it's available over the network and can be configured through a web browser.
I was with you until this point. A Pi hasn't been easy to source for almost 4 years now.
This is already a job that requires fairly decent electrical knowledge, especially if there are 3-way switches involved.
Turn-key solutions exist for people that don't want to deal with the complexity.
For someone who doesn't have a Linux background, "just put it on a Raspberry Pi" is kind of like saying "You write a distributed map reduce function in Erlang". Ie: it's easy if they know it, but if they don't then that "just" is doing a lot of work there.
Pre-installed is almost certainly the way to go for such a person.