I noticed that here on meta there are many Film/TV show and franchise tags, like:
On the main site they make sense but do we really need them on meta too?
Meta is the place to discuss the workings of the site itself. Inherently questions on Meta are not about a franchise or work.
This is why Meta has one of four required tags (support, feature request, bug, and discussion).
But not because of the franchise.
We tag questions on meta with tags that describe what the question is about. That's what tagging is for.
For some of the larger or more complex tags on the main stack, the need can arise to discuss these main stack tags (or the questions in it). Examples of these indeed include star-wars and star-trek, which both have numerous sub-tags and thousands of questions, but also story-identification, which isn't a franchise, but still has a meta co-tag for its main stack tag.
This does not mean that every tag on the main stack should have meta counterpart, nor that every "large" tag on the main stack (for varying definitions of "large") should have one.
Only those main stack tags that are begin discussed on meta in several questions, may find a co-tag on meta useful.
Sometimes meta questions are specifically about a particular franchise, even requiring expertise in that franchise in order to be answered: see for instance Star Wars/Canon/Disney Revisions or Which canonicity is more right in a Legends question? in the star-wars tag. Just as issues surrounding story-ID often need special consideration that other tags don't (hence not only our story-identification tag on meta but also similar tags on other sites' metas), so might issues surrounding, for instance, Star Wars or Star Trek. These massive franchises, taking up a large proportion of questions on the main site, are valid topics of meta discussion for our community.
Besides, what harm do these tags do?