I don’t know why FA chose the Pi in the first place but I suspect it had to do with universal availability, reasonable price and a stable and suitable operating system.
I’m just making an educated guess but by far the majority of those running a feed to Flightaware are interested in something other than ‘playing around with Linux’. (Puts on tin foil hat and ducks for cover).
The difference between a $15 and $35 SBC is trivial for most ADS-B feeders but time is much more precious. It takes less than an hour to go from a pile of components to an installed and reporting receiver station with a Pi and the piaware image. It is even easy enough to talk someone half a world away through the process over the phone.
I have three Raspberry Pi that have been running the Piaware image, none of which has been touched for two or three years. The antennae, amplifiers and filters have undergone many iterations because that is my area of interest.
but a replacement Pi 3B+ would have been a 30 second upgrade.
Most importantly, FA now only have to support one image rather than one for each SBC manufacturer and each of their models.
About 6 months ago someone suggested that FA would get twice as many feeders if the provided an image and supported all the old x86 computers looking for a purpose. A read of this thread gives a pretty good idea of why they are not supporting other devices when the Pi works so well.
YMMV
S.