While SEAT and Skoda don't have a huge market share when compared to VW and Fiat, they're each considerably larger than Lancia or even Alfa Romeo. In Europe last year, VW sold 389,255 SEATs and 246,378 Skodas (according to JATO Dynamics) while Alfa Rome sold 170,785 and Lancia sold 108,529.
Also, Bugattis "don't sell much" is an overstatement since there hasn't been a new Bugatti built for public sale in years.