Defects is a metric businesses doesn't care much about. If you have a good team that can create products customers wants, then it is better to have them keep making new products rather than maintain what they already have, then you can have less productive engineers perform maintenance, defects might go up but this way you will have way more products which businesses seems to care more about.

You would have a point if maintenance was something companies cared deeply about, but they don't. They want new products, and company specific knowledge doesn't seem to be very valuable there.