Biggest reason is the price.
The 3 series used to be a low $30k car.
You can't get a decent 328 under $45k or a 335 for $55k.
It creeps into 5 series territory.
Heck if I were to spend $55k, I'll add 5k to get the M3 instead!
2011 535i Alpine White, Oyster on black interior, Premium 1 & 2 Package, Magnaflow Full Cat-Back Exhaust, JB4 Stage 2