Dordle's solution is kept under local storage, any user can access easily. right click + inspect --> Application --> Local Storage -->   under the last_free_game key you see the solution.

...Why would this be an issue for the average player? It seems like anyone doing this would only be spoiling themselves

Surely you could more easily (for the average player) just open an incognito tab if you're going to cheat yourself? I don't see what this solves?