Most project managers don't have a formal education. Unfortunately, they need to collect bits and pieces of knowledge all over the internet.
Sometimes, it feels like you need to fly an airplane while still building it.
Moreover, there's a huge gap between the theory and practice of project management. You can spend hundreds of hours and thousands of dollars on certifications, but still, you won't know what to do with all this knowledge. You won't feel confident about running a project in a real company with a real team.
That's why reading Project Management Institute's PMBOK® Guide is not the best option. It's a great book, but it's an encyclopedia. You don't take one to solve practical problems.