At average apparent text sizes, you only see ~4 letters clearly at a time, so it’s often enough that you can’t read a whole word at once. From there, there’s so many prefixes, suffixes, conjugations, compounds, and portmanteaus that it doesn’t make sense to just try to memorize the dictionary. What happens when you’re reading a flamboyant author that has tons of theasaraus usage and you come across words you’ve never heard in your life? You use context as best you can, but if there’s familiar roots in the word, you have a better chance of understanding it.

Also

spelt

That is a grain spelled “spelt”