That's exactly the point. The article explains why it was such a technical challenge.

“And this problem was unpredictable because it depends on three things,” he continued. “It depends on the shoe itself; certain shoes will flex more than others. It depends on how the cleat and force plate are fixed to the shoe; in other words, where exactly they are. And lastly, and perhaps most importantly, it depends on the rider’s pedaling style, because some riders will flex the shoe more than others. It was a big problem, and we only got to that point within the last two weeks.”

It could be fixed in theory, but that would make it cost a lot more and I'm not sure people would opt for such a product over traditional PMs when it's likely it would go out of calibration far more often.