Did the video card manufacturer test the old 12VHPWR connector or install these components without testing?
I read that the problems were due to poor-quality contacts, among other things. If the new connector is made from low-quality elements, then we may see a repeat of history with the 12VHPWR connector.
They probably did and it turned out to be fine. However you know how it is, until you get a mass distribution you can never tell if something is reliable or not. Take cars for example. Manufacteurs put in billions of dollars of R&D and they end up having to recall many vehicles leading to billions of dollars in losses, obviously they wanted to avoid this but they couldn't because you cant really get a real world exposure during their R&D testing phases.
The same happened with all these GPUs and power connectors overheating. It was up to code but it was failing anyways for other reasons. Poor contacts or poor conductivity materials could be one of them.