I just have a really hard time believing that anyone actually brush their teeth 3x a day

Try having braces. You have to otherwise people constantly remind you what you had for lunch.

My dentist basically said once a day is fine but I’ve always done it in the morning and before bed.

Definitely twice. Occasionally 3, depending on what social plans I might have during the day.

Just brush the teeth you want to keep 😆👌🏼