I think it's a multitude of problems.
Large company such as Polk should have no difficulty at all designing great sounding loudspeakers. They have resources, finances and knowledge to do so.
The main problem as I see it, is not giving a flying duck about the end result and trying to compete with cheaper brands. This rat race for a budget speakers brings bad results. Polk use to be known as a good company, manufacturing good speakers and as far as I know they hold a few pattens. Now they are just another cheap brand, made in China.
I've been in woodworking and manufacturing for the last 15 years and I have too tell you guys, manufacturing in US can be done efficiently and profitably. Quality control is also way better.
It's then the company trying to squeeze every penny, lets go of a reputation, then it's a problem.