If he joins Shitty or Chel$ea, then we're talking simply money reasons obviously and then he can go fuck himself and hopefully become a Moriba 2.0.
If he chooses a team where he actually gets playing time, then I'd understand his decision, because he has normally 3 young players with Olmo, Fermin and Gavi in front of him, so getting any minutes will be near to impossible for him and with 18 years, you need to get them.
But Masia had always this problem with too many talents coming and you can't keep them all, especially midfielders grow literally on trees in Masia. The other problem is, that Barca Atletic plays in the 4th league and you can't convince any good talent to waste his time there.
And with the release clause paid and a bit more space from MAtS going on loan, maybe there'll be enough ffp room to get a CB.