It has WiFi, which requires FCC testing for the US market as well as compliance certificates for the European area. These certifications and checks are f...ing costly.

RPi/Arduino in contrast only have wired or no networking, thus eliminating a huge part of the upfront costs (e.g. in Europe you then only need a CE certificate, which you can either issue without testing and be liable if your module doesn't meet the standards, or you get an ESD/EMR test for a couple thousand bucks).