Unity started with pretty awful performance (much like GNOME 3) and coincided with some infamous decisions on the part of Canonical, namely that whole business with the Amazon integration, so it’s permanently tainted in the minds of many. It also meant that the largest distro in town was suddenly using a desktop that was much less inviting to newcomers than the familiar GNOME 2.
I’m glad it’s being kept alive as it does have a unique vibe to it, but I always found the workflow a bit awkward and much prefer GNOME for something modern and xfce or MATE for when I want something traditional.
What you’re asking for is distributions to roll their own solutions instead of contributing upstream to make it better for everyone. Distributions and the organizations behind them frequently do things to make the user experience better, it’s just that the preferred way to do this is by making the projects they use better…which will just look like a DE version bump by the time it makes it to a distro changelog.