I don't know, but I guess that the intricacies of tax law are written down. And to study that (https://www.law.cornell.edu/uscode/text/1/112b here?) you need to be able to be quite proficient at reading. And usually proficiency at efficient reading of laws translates to an ok command over speaking/writing as well (which apparently is not the case here)... if you read weird words a 100 times, I expect a moderately intelligent person to remember how to spell them...

I work in tax. Yes, you need to be able to read and write well to understand the changing tax law in the US. The tax code is also used as social policy in the US, and it's important to know for liability reasons that even the person you're paying to do it for you is doing some parts correctly. Did your payroll employee not withhold key taxes? That's a pretty large headache and fine you have coming.