The Google Style Guide says:
Ordinarily, functions should start with a capital letter and have a capital letter for each new word (a.k.a. "upper camel case" or "Pascal case").
For me, Pascal case looks very unfamiliar and I'm very reluctant to adapt to that guideline. What is the style guide's reasoning behind using PascalCase?
It's a style guide, which is opinion based. If you don't like it you don't have to follow it. Function names can be all lowercase, all uppercase, or 90's chatroom style every other letter uppercase! The style guide is just a preference that produces consistent, readable code.