There's an astonishingly large ecosystem of widgets, extensions and additions and having a single point of integration that (mostly) everyone agrees on allows them all to work fairly well together.
There are things that I wish could be improved about the admin - mainly to do with the slightly old-school HTML and CSS behind it - but there are so many points where you can override, replace and extend that the good outweights the bad.
I use this: https://github.com/django-admin-bootstrapped/django-admin-bo...
It seems to work pretty well.
Unfortunately - there is a limit to how much you can alter the admin HTML without this problem. My own admin skins have been CSS only precisely to avoid this.
I am currently trying to learn the ins and outs of generic views with djang-extra-views, so that I can hopefully do as much, but without the restrictions of the admin.