There are a lot of reasons here which are correct, but one huge Factor when I was working with custom roms was the fact that the actual underlying hardware driver and firmware were a black box. Generally speaking you would need to harvest the binary files that made things like the camera, gps, and/or touchscreen work. Sometimes it wasnt too hard if you were going from one android skin to another that used the same underlining operating system, but if you wanted to make serious changes, and the phone manufacturer wasn’t great at sharing, it could take a very long time to figure out what data needed to be passed to the camera to make it turn on and be available to use. What got even worse is if you wanted to upgrade your android version (5 to 6 lets say), where android made serious changes under the hood, you ran the risk of having these blobs not even work with the system. They would expect something that android no longer passed or provided. Or they were using some deprecated API to make their function a accessable. It just became impossible to do without being able to recompile the binary only portions that weren’t subject to the gpl. As android has gotten more security conscious it has made things even more complicated.

There are a bunch more then 2:

Acer rog handheld Lenovo legion Gpd win 2/3/4 and various versions Ayaneo has a few different models Onexplayer which also uses an Intel chip Any loki

There are probably more, I haven’t used any of them so don’t take this as an endorsement of any of them…

Most can bind it an IP even if they don’t bind to an interface. I use rtorrent and airvpn/wireguard. Wireguard uses a static IP address for the client and rtorrent can bind to that IP. If the VPN goes down (which is very rare in my experience) rtorrent stays running but it won’t work on any other IP address.

I installed 1.0… all 23 discs that I downloaded at 2400bps because I couldn’t afford a faster modem.