If the EV is close to being completely escorted, the defense should react accordingly.
You may not agree, but this is what I refer to when playing defense - planning 1 step ahead for the next phase when it is nearing.
Lets take a look at other examples too:
Terminal: When the wall is about to blow up, the defense should be setting up to defend the opposite side of the wall if they have already lost flag. If they still have flag and are spawning on the same side of the wall as the C4, they should be setting up to ensure nobody slips through the wall as soon as it blows up and gets quick plants on the containers.
Trainyard: When the trackswitch is about to blow up, the defense should be setting up to quickly switch to the armored car plant - or hunting down any offense players that quickly ran through as soon as the gates opened.
Or if you are more familiar with Football than Objective based First Person Shooters:
4th down with 1 yard to go: Defense will still have one player in the secondary covering a long pass attempt for the JUST IN CASE scenario.
Apologies for being blunt, but what you described is players just simply not playing smart.
On pub servers this definitely can occur more as it is just that, pub servers.
In setup 5 on 5 organized competitive playing matches or scrims, you will see more competent play that this would not work on - or if it does, it then again means - that the offense was either that good or the defense fell on its face and was not planning 1 step ahead.