Also, NVidia and Cuda drivers mess the upgrade path as well. And ubuntu is the most supported distro.
Actually you can upgrade from old releases. You do need to move from LTS to LTS, rather than jumping. So you can upgrade 14.04 to 16.04, then to 18.04, and then to 20.04.
See https://askubuntu.com/questions/91815/how-to-install-softwar... for details.
They seem especially hell-bent on pushing new versions of CUDA on everyone way before any usable software supports it (i.e. try getting a usable tensorflow or mxnet when your machine auto-upgraded to 11.4.x one day after its release).