Why are there no botique car audio recievers?

Burmester for Porsche, B&O for BMW, Mark Levinson for Lexus

I look forward to read some of the answers of this thread, good topic, cheers.

Not enough cash in it I guess. Maybe more will pop up in the advanced audio sector in larger cities. Not exactly sure!

I managed in the auto components sector for many years. The money is in OEM. When I was with Delphi, we had a relationship with BOSE and Sonigistix (Monsoon audio). Back then, the premium system were just speakers while we (delphi) built the head units (or we sub contracted to Pioneer), amps, etc. BOSE would provide Powered speakers which would be hooked up to a standard head unit (GM Cars). The 1999 Corvette I owned had the same head unit found in a Chevy Lumina with powered BOSE speakers. 

Nowadays, I'm not certain how everything is done. 

Me either, but I had a Bose system with what looked like a Pioneer  head
in a Nissan Maxima .
Sounded great !