Wordle works with a 12k-word dictionary, which is very much comprehensive (that includes "words" like "grrrl"). However, the hidden/secret words are picked from a much smaller set of 2k reasonable words (i.e., frequent ones, and that most people would describe as English words).
There are two reasons that you always win within 6 guesses:
1. It has been shown [1] that in hard mode you can always solve wordle in 6 guesses (but not always in 5) if you assume that the hidden word is "reasonable", i.e., taken from the 2k-word list. However, if you know 12k 5-letter English words and if you don't assume that the hidden word is "reasonable", then you will sometimes need 7 guesses.
2. Even then, the average number of guesses that you need is much lower, at 3.5 guesses (or 4.5 using all 12k words). So if you play optimally or close to it, it is only in very rare cases (the worst case) that you will need the full 6 or 7 guesses.
So, surprisingly, the game is easier if you are not a "savant", or to be more precise, if you are not a computer :-).
[1] http://sonorouschocolate.com/notes/index.php?title=The_best_...