They probably weakened the magnet to make it detach more easily to prevent the point where the plug connects to the wire from weakening over time, which is a battle that they (and other laptop producers) have now been fighting for many years. They've had multiple class action lawsuits about this same issue, and multiple recalls, and they still haven't been able to get it right. I personally owned multiple models that ended up producing sparks because the wires inside had gotten so badly frayed.
I reckon it's a genuinely tough engineering problem, since besides unintentional yanks, a laptop power cord gets plugged in and unplugged and hauled around in bags. But it's pretty surprising that they haven't been able to make this enough of a priority to solve it, given how much they charge for those adapters and how much they must have lost on recalls and lawsuits.
But honestly, the solution is simple enough: make the side that gets easily damaged replaceable, and let customers have free replacements every 6 months (and build that trivial cost into the original price of the adapter).
I reckon it's a genuinely tough engineering problem, since besides unintentional yanks, a laptop power cord gets plugged in and unplugged and hauled around in bags. But it's pretty surprising that they haven't been able to make this enough of a priority to solve it, given how much they charge for those adapters and how much they must have lost on recalls and lawsuits.
But honestly, the solution is simple enough: make the side that gets easily damaged replaceable, and let customers have free replacements every 6 months (and build that trivial cost into the original price of the adapter).