No supplier of android boxes running the amlogic s905 chip has successfully developed a fully functional firmware with android 7 or 8. Ugoos had a firmware for their am1 machines but they do not support ethernet connections. Users of other machines who tried to load that f/w found it broke their WiFi connection.
Technology moves on. In the world of android boxes, chip manufacturers do not make chips that will support every new version of android going forward. Sad but true. I suppose a comparison is to Apple devices where older machines like my old iPhone 4 cannot run later versions of the apple os, meaning I cannot run many of the apps I want like Google drive, WhatsApp video calling and so on.
It should be reassuring for you that I have a Droidbox that still runs android 4.4 and does everything I want. So the need to keep fully updated with android versions is overrated in my opinion. (I don't work for Droidbox btw)