This is the age old problem we've been having since Higuian and Ronaldo.
We should be the team getting these guys BEFORE they take the Bayer or Leipzig step. That should be them stepping to us and going from 10-15m buys into 60-80m values.
We act like we're still at the same level as the Madrid or Bayern or any of the EPL teams.
Our strategy seems to be focused on being that stepping stone for players playing in Italy. Some of them cheaper than others, but what you describe is what we've done with Gatti, Cambiaso, Bremer, Di Gregorio, Locatelli, Chiesa, Dybala, Vlahovic and others too over the years. Weah and Conceicao are examples of this from abroad as well.
Most of them haven't really worked out (yet?) and that's probably in part down to the players but imo largely due to our headless management, training and development structure. But we are trying. This was supposed to Giuntoli's speciality but we've yet to see it much.