Agreed, but they're directly strengthening a PL rival. I'm sure their first preference would have been to sell abroad, and it's not like Matic wouldn't have had plenty of suitors. I'm sure a few would even match the 40m fee. According to the Sky Sports Article they're letting him come to us as a goodwill gesture for service, similar to how they did for Cech. This suggests the sale is sentimental, rather than the money. If it was the opposite situation I wouldn't want Matic going to Chelsea under any circumstance.