They did:
Here is the joint position in December. Article 50 (Oh, the irony) on the backstop solution indicates now regulatory barriers.
https://ec.europa.eu/commission/site...int_report.pdf
This is Davis two days later:
https://www.theguardian.com/politics...er-brexit-deal
We are talking international relations and negotiations here. When you reach such an agreement, both sides expect to be able to put it in legal terms and move on.
So far the UK has not looked united, reliable or trustworthy in any of this.
edit:forgot the first link