The descriptions are available by clicking the info button on the top right of the tag page (this appears as a wrench to edit the tag for admins)… for example, on official
We do have a theme component that showcases the tag descriptions in banners: Tag Banners
I’m not sure if this is something we will want to do for performance reasons… though @tgxworld or @kris.kotlarek might have a better idea of whether or not it’s possible.
The difference is that categories are much smaller in number and admin-created… we do not expect a site to have 1000 categories, and if one did they’d hit performance issues because of how much data is serialized for each category (descriptions, colors, a bunch of settings, etc). Tags on the other hand may be user created, and we expect the possibility of thousands on a site… so we’re usually only including their name and ID in most places.