Its simply not economically viable to design and build a car in today's market that is geared towards such a relatively small market like people who would buy a true muscle car these days. No features, no power anything, no AC... sure, some would sell, to the hard core people. But the R&D and implimentation of a car design is not paid for by that sized niche of the market, unless its priced in the 'exotics' territory. The sales figures required to keep a model in a range the average person can afford means also appealing to women driving their kids to school, middle aged guys commuting to their office job, etc.
Remember guys, even the 60's "muscle cars" came in 6-cyl versions.