The M3 has been an overall sales failure since 2008, no matter how it is spun. It used to be that the E46 M3 sales (Coupe and Convertible) in the USA alone was around 8000 a year. Now it barely exceeds that worldwide.
That's messed up.
With that said, that sales failure is not because of any inherent E9x M3 deficiency, it is just that between the economy, the fuel economy concerns/prices and the jump into the $70,000+ bracket -in the USA- it simply tanked, IMO.