Bring back Adobe Color Themes!

Software development is really complicated and there's a lot of unexpected inter connectivity. I don't have any information on why the panel was removed, but one common reason features are removed is because they need to be tested regularly, even if their code isn't necessarily being updated. It takes a lot of work to maintain old features because they may break when new code is implemented in other areas of an app. The Color Themes panel, which stayed in the software largely untouched for a long time, might have relied on an old version of a component that was slated to be updated. Since the panel wasn't being updated to incorporate this new version of the component or library, it would break when the new component was added to After Effects. Again, I don't know the actual story behind this panel's removal, but what I described above is very much a real scenario that has happened plenty of times before. 

Its crazy that it was killed, it was so useful! I'm not sure why can't they just leave it in and if they don't have capacity to update it then just leave it as it is.

It doesn't seem likely. The panel was officially killed back in 2021: https://helpx.adobe.com/x-productkb/multi/eos-color-themes.html

I agree, though, I really liked it and was disappointed to see it go.