Young players such as Yamal, Gavi and Pedri are a great advantage for Barcelona, which has a bad financial situation. If they sell them at the right prices, the club can become economically stronger. In addition, quality football players are constantly emerging from the infrastructure and by selling them, the club can earn additional income. Yamal is a good player, but I think it would be better for Barça if he brings a big transfer to the team.
The Barca president and management are not stupid, if they received an offer of 200 million and didn't sell it, it means they think they can make more money from the player or achieve more success from that team. Frankly, it would be difficult to sell a 16-year-old wonderkid, perhaps the greatest talent after Messi, for 200 million and watch him 20 years playing for another team. Perhaps Yamal will gain much more than this, both financially and in terms of success, during his time playing for Barca.