Too many people were getting the impression that OP_RETURN was a feature, meant to be used. It was never intended as such, only a way to "leave the windows unlocked so we don't need to replace the glass when someone breaks in". That is, to reduce the damage caused by people abusing Bitcoin.
That doesn't make sense to me.
On one hand you're introducing OP_RETURN to stop hackish and inefficient methods to store extra data in the blockchain (like using multisig outputs). On the other hand you reduce OP_RETURN to 40 bytes and say that it was never meant to be actually used thus forcing people to continue using their hackish solutions.