And one theory/perspective is that May (with the background of a home secretary) was focused too much on that and drew lines in other sectors without enough consideration for the consequences she then had to try and walk back, which put her always on the defensive against the hardliners, which made a positive framing of a closer-aligned deal impossible. It's fascinating how that shift from "Brexit means a wide range of options and people voted for something of it" to a pile of red lines blocking out a large range of the solution space happened - apparently even to the surprise of members of the government.