Yeah it's already been established that they've got the best deal they can... with May's ridiculous red lines. The EU would be open to negotiate if they felt it was an actual negotiation and not May standing firm on her demands and expecting the EU to concede on other things.
Yup, it's even clearer when you look at what Heiko Mass says, he said that delaying Brexit would only make sense if there is an actual chance to reach an agreement which at this point in time is unlikely, he added that he doesn't believe that there is actual room for negotiation anyway.