It’s not a secret! We can talk to our bros about supplements!
BCAAs get absorbed into the bloodstream for use in your muscles, rapidly.
Protein contains the BCAAs and the rest of the good stuff. But the BCAAs are “bound up” into the structure of the protein. If you have some “complete protein” Your body needs to break the BCAAs loose (partially digest the complete protein) to make them available.
If you use just the BCAAs you get to skip a step, and fuel the muscles right away.
This. Hence they are usually taken post-workout