Strain relief is, or can be, somewhat ugly. More angles, thicker cables, varying widths - it all adds up to muddying the lines of their product.
Compared to how much they make on device sales - selling a few more adapters is peanuts. How many people do you know that have downright dangerous cables which they persist in using? I'm sure I know dozens.
But despite the obvious advantages, the next generation went back to the old design, but a little bit smaller, and back to all the old issues. I probably spent a few hundred dollars on replacement 3rd gen chargers alone, while the 2nd gen charger which came with my laptop is still in perfect working order in a box in my closet.
The cynical of me honestly wonders if they didn't see a decrease in peripheral revenue after the first iteration, and reverted to the old design only because of that.
As they make a fuck-ton on resale of these accessories. (planned obsolescence)