I’m going to have to disagree that USB and serial fobs are a moving target. Neither require direct support of a specific device, as both have robust and stable abstraction layers. That’s precisely why they are so popular for makers/hams/etc… tty serial hasn’t changed in any major way in linux since… the early 1990s? And Alsa has been around since 1998. ASL doesn’t even have the burden of supporting multiple operating systems that complicates these hardware abstractions.
As to the cost - If I could use any old USB fob ($3 for $10) and the built in pi serial interface I could build an entire duplex node for less than the cost of a URI, and still have overhead on that pi to add a second node (about $25), an RTL-TCP server ($20-30) and probably more.
This is also a bit of a privileged point of view. A lot of our community where I live struggle to afford the cost of a decent radio, or a QTH that allows them a usable antenna in an RF friendly environment. For them that $50 or $70 could be the deciding factor for a friend building them a node with the pi 3 they just replaced with a 4b, or the difference between saving for a few months to build a node and deciding it’s too expensive. Fortunately, we have echolink to offer those people, but echolink has numerous disadvantages, which I am sure are well known here.