The journal is about a thing this person does privately for fun.

The writing style is clearly not meant for others to read either. They just did stream of consciousness out of their brain and didn't proofread. It's not meant for external consumption.

Capitalization is something you do out of respect for your reader, to make things easier for them. If you aren't intending others to read your writing, then there's no one to disrespect, so why bother?