Oops this bug is invalid, I read somewhere that vanilla blocks cannot be overwritten.

Original bug:

In the Minecraft addon page, there are vanilla resource and behavior packs available for download. But the vanilla behavior pack doesn't contain any of the block files.

How to reproduce:
Go to minecraft.net/addons
Download the vanilla behavior pack (It's found when you scroll down a bit)
Look inside it and try to find any vanilla block files ❌

What I expected:
There would be vanilla block files that I could modify to create an addon

What I saw:
The block files are not there, only the entity files and other stuff