Grade Master3 cartridge--Moving Iron Design

Posting this because I just bought my first Grado cartridge since my entry level MM decades ago.I chose  the Master3 because it was highly rated and I was intrigued by the Jarrah Wood, boron cantilever and the nude elliptical stylus at a $1,000.00 price point. It's not the most expensive cartridge I have mounted on my VPI Signature table, but it has an excellent balance. Have run it about 20 hours now and it has settled in.

My question is the moving iron system is an excellent design and why haven't more manufacturers seen fit to utilize it?