The EU has spun negotiations as if they were contractual to dodge the reality of a Treaty. It poses as buyer and the UK as contractor demanding its terms of offer and contractual rights to consideration (payments) along with rights to compensation. Treaties do not work like this

Thus it can play the aggrieved party treating the UK like a rogue contractor. It is much like a supermarket demanding suppliers pay to display their goods and take compulsory lower prices when the supermarket demands them. The EU has skillfully dodged the courtesy of equals that

is necessary to negotiate and create firm and well founded treaties where parties hold common respect for each other. By posing as the buyer, the EU is trying to subjugate and crush what it views as a dishonest and dangerous contractor. That insult is warning enough to walk away.