So, the way the categories on explore work, is we have a default list (admittedly from years ago where we first started) and that is used to append to the dynamic list where the dynamic list doesn't have items (if there aren't enough unique categories being tagged by current liketu users)
We will probably do a lot more tweaking to make these context aware. For instance, in "My Feed", the categories are procedurally generated by the categories most used by the people you follow, and if you click on anyone of them, then its the most used categories that are most commonly used with that one. It probably looks a little bit repetitive but we designed it with the assumption that eventually the platform and it's users will have more than enough posts to fill those up.
I personally would like to "explore" more ways of delivering usage dependent categories on the explore page, but we don't track browsing behaviour, only chain behaviour, so we'll have to think about how to go about making that more feasible.