Because I'm cheap.
Actually I wanted a car that was somewhat of a jack of all trades, fun to drive, reasonably luxurious with modern tech features like Nav, a decent sound system, a reasonably usable rear seat, enough luggage space for Costco runs. I also liked the idea of a retractable hard top as it gave the advantages of a coupe and a convertible.
Owning a BMW is not something that I aspired to and I have no particular loyalty to the brand. Quite frankly if I had know how poorly the sport suspension with the RFTs was sorted out I never would have bought it but at this point now that I have ditched the OEM RFTs for Cont DWS and have installed Koni FSD dampers I am happy with the car.
Not sure what I will replace it with when the time comes. Practicality is no longer that big of a consideration since we purchsed a 750Li earlier this year.
I will certainly look at the new 4 Series and M4 but I am also interested in the new Jaguar XF.