Well it is impressive, but it appears that the swimmers know in advance that they are going to break the WR and have such certainty that they are not surprised when when it happens.
I was watching Katie Ledecky destroy the field by a huge margin while going out well above WR pace. My running brain was worried that she might falter in the end and lose the gold medal, as happens pretty frequently to runners who try that. I was wondering why you would risk it when you can get a WR at any meet but an Olympic gold medal in only one. I concluded that swimming performances must be more predictable than running ones. Maybe it is the lower impact nature.
I also thought about how swimmers cannot gain a big tactical edge by drafting or staying at the back or pacing off a key adversary because they are in lanes and cannot see well enough to precisely judge the overall race situation. No looking around, everyone within 1 sec, no visible jumbotron, and tough to hear the coach shouting instructions. It puts a premium on going as fast as you can.
Imagine if you ran a championship 5k and every runner ran separately on his own track all alone with no info about what the other runners were doing and no reliable info about pace or opponents times was available. What would you do? You would even split it at as fast a pace as you possibly could maintain. You would really go for it and if it was the most important race of your life you would likely run a PR or very close to it. The winner would be under 13 min, every time. Swimming is like that.