I know it has been decided not to have tags exclusion because "it is complicated" (probably because of T166618: Handle more than 500 tags per wiki?), but I'm creating that task to have clarifications about that. Also when the possibility to exclude some filters will be available, you can be sure users will ask to have it for everything. :)
Following this discussion, imagine if a wikis has 79 tags: you have to select 78 tags to display all tagged edits except ones filtered by a particular tag. This is not simple.
Another solution is to have a filter that would filter "all not tagged edits", so that people can select a little set of specific filters and add all others.
There is already a way to exclude Namespaces, which could be an inspiration. However, this system is binary: you can include namespaces OR exclude them, but it is not possible select some but exclude others.