Nothing stops the big box stores from carrying these products now except for a couple minor issues.
1. They don't want to.
2. The customers don' want it.
3. The sellers don't want it.

Imagine Joe Ordinary: "Why is this Conrad Johnson $5,000 when the $159 Pioneer has the same watts, more knobs and those cool blinking lights?"

Salesman: Picking his nose and scratching his butt, " I dunno, I'm just here on summer break and they made us promise not to say anything useful." "I own the Pioneer, it's just great!" "Over here are some $139 speakers you could listen for yourself and decide."