Question: Why the single file?

[AndrewOt]

I was browsing the source code because I was curious how the <Form /> component works and discovered all the code for react-router code is in one index.tsx file. I'm simply asking what the reasoning for this decision is, given that most other repositories I've browsed or organized myself are broken out to be one file per component and follow some neat file structure to lead the read to what they are looking for.