This is probably for an audience less enamoured with the Pi than the HN crowd. Someone that's more interested in getting to a working result than having to yak shave for a couple days or more to do the same.
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.
When it comes to Home Assistant, the Pi is actually a much more pragmatic option.
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.
Keep in mind that Home Assistant provides ready-made images that behave like an appliance and can auto-update. In fact, it doesn't even give you a shell/SSH by default and such access is discouraged.
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.
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.