Talking about frontier mathematics? Even the common for-mere-mortals version of mathematics is totally inaccessible to most people. Even to those who want to really learn it.
Take a good look at the textbooks that teach mathematics and tell me I am wrong.
Whether intentional or not, it's there. I have yet to see a textbook that really taught learners as they deserve to be taught. Some are good in some aspects, but a perfect textbook does not exist.
"Here are some theorems and some proofs and here are some ideas left as exercise to the student". smh.
I am well aware of all the sites and YT, what you probably thought I live in a cave? I taught mathematics at Tsinghua for over a decade, so I know what I'm talking about.
3B1Br is great but only for a 'hobbyist'. There's no systematic progression to teach from A to Z. Also, you can't learn mathematics just by watching videos.
Take a good look at the textbooks that teach mathematics and tell me I am wrong.