Not every episode necessarily but they would have to be familiar with something like 30 characters, multiple species, IU events and such.
Which is apparently too much to ask from people.
But why though ?
Why would any new viewer have to be familiar with anything that has gone before. Surely it wouldn't be asking too much for any post Voyager Trek to be a brand new show that people are able to jump into and enjoy whilst having absolutely no knowledge of any Star Trek shows prior ?