"Reducers" come from the similarity with the callbacks passed to `Array.reduce()`, "thunk" is an existing CS/programming term, and "saga" was also adopted from the backend world. So sure, a lot of these terms are new to most people (especially front-end developers), but they were generally based on existing terminology and not just picked out randomly.
It reminds me of Haskell, where monad is such a terrible name. Same with functor, applicative functor, etc. Yes, all these names aptly and mathematically describe what they do, but the most precise name will not help beginners understand.
For instance, if reducers were called "state updaters", I think people would be less confused. Same if "map state to props" was called "get props from state".
Sometimes you gotta give up on giving the most precise name and instead give a name that is the most clear for the greatest number of people.
Many programmers are bad at naming things. Many are bad at doc. None of this stuff is actually hard, it's just made hard and made unfriendly in unfortunate ways.