It's using one of Phu Ly's WordPress themes from 10 years ago so that may be why. I'd recognize his themes anywhere. Back then 8pt was standard and flexible units were just catching on. I feel old.

Yep, nearly to impossible to read without a big zoom. The culprit: font-size: 62.5%;

Sorry, I don't remember if I've ever actually configured the Wordpress settings on that blog.

A good time to try out your browser's Reader Mode. :P