I read that it's to do with FFP and the wage bill. Loan transfers do not count against your permanent staff wage bill and FFP states that the wage bill cannot go up by more than x% per season. The Ozil deal (amongst others) means that we are very close to the x% threshold and face a fine if we do buy permanently in this window.
If we swap Ramsey for Benatia that will work as Benatia will offset Ramsey's wages.