We're in agreement on pretty much all of that...
Whilst they may have pax lists from carriers and shipping companies, this is all second hand. So, I do not mind that they do not check departures, but they have not done what they said they would. Which seems to be the way of so many modern politicians.
It was pretty obvious to me early in the Covid outbreak that the government would put responsibility and costs for checking paperwork/tests onto the private sector (specifically the operators, and most specifically check in and gate staff) ...they weren't gong to spend an extra penny if they could help it on providing extra Border Force staff to check passengers inbound and/or outbound.