Teresa May was a remainer. David Davis was a leaver. So although he was appointed Brexit Secretary, May surreptitiously undermined Davis by giving Robbins effective charge of any real "negotiations". Davis had had enough of this bs by the time May came back from Germany in July 2018 and he quit. May should never have been PM.
The "Brexit done" rush was all about Boris's determination for a Brexit conclusion by end 2020. An ego thing probably. As you say, this TCA is probably better for the UK than nothing, lousy as it is.