My Future stars evo isn't icon chem after cosmetic upgrade

Try to understand how rarity (i.e. card type) works in the game.
The cosmetic evo card does not give you a chemistry boost whereas Future Star Icon card gives you a chemistry boost.

How come that i can upgrade my Bale Maradonna card with a fut birthday 19 cosmetic but still keeps his icon chem?

Icon and Hero chem boost works differently than normal player. Icon and Hero cards have separate clubs and leagues.

Future Star Icon, Grassroot Greats, Globetrotters etc. cards chem boost works based on their card type i.e. Rarity.