Transfering players aboard younger than 18 years old

I still have difficulty understanding why we can not transfer players younger than 18 years old to a foriegn country. This is possible with the parents permission. I mean the most clear example is Messi and there are many more examples. If the player and their mentors thinks, it is the right club for him, why not? Player's parent or mentor can decide by the clubs reputation, training facilities, youth academy, etc. I think SI needs to add this to the transfer system.

What do you guys think?

Messi moved to Barcelona years before the U18 transfer ban was established.

Messi moved to Barcelona years before the U18 transfer ban was established.

I understand but I know first hand that Barcelona still scout players at young age. How do i know that? My friend's close friend's 14 years old kid got contacted by Barcelona and he was offered to move to Spain with his family. They actually traveled to Barcelona to visit their facilities and all expences paid by FC Barcelona. This kid is extremley talented. However his family felt they and him won't be able live aboard. This happened in 2010. So, this is the example I know my self first hand.

It is my understanding that the game simulates these types of young recruitments by having foreign players appear as new regens from your youth system, if your facilities and recruitment network are sufficient. Transferring a player who is already within another team's youth system probably falls into another legal category. You can still sign young players from abroad, but most transfers do not go through until the player turns 18.