Why such a commonality? You guessed it: The DeLorean was also designed (or rather re-designed) by Lotus under the watch of Colin Chapman, as Aaron Severson explained in detail in his excellent history of the DMC-12 on Ate Up With Motor:
With the British investment, DMC’s future looked bright, but the car itself was still not ready. To the frustration of Bill Collins, the second prototype, built by Detroit’s Creative Industries, had been a poorly finished mess. With groundbreaking on the new factory slated for October 1978, Collins admitted that DMC needed outside engineering help.
Collins and DeLorean approached Porsche and BMW, but both companies wanted far more money and more time than DMC could afford. DeLorean then turned to Colin Chapman of England’s Lotus Group, which had considerable experience with plastic bodies. That fall, Chapman signed a contract for Lotus to re-engineer the DMC-12 for production.
The DMC-12 project was a major undertaking for Lotus, involving more than half its modest staff. Since time was short, Lotus engineers discarded much of Collins’ original design, substituting features from the contemporary Lotus Esprit. The biggest casualty was the ERM plastic body, which was replaced by a two-piece fiberglass structure using Colin Chapman’s patented Vacuum Assisted Resin Injection (VARI) process, licensed from Lotus at considerable cost. Because fiberglass lacked the strength and rigidity of ERM, Lotus was obliged to add a steel backbone frame, similar to that of the Esprit. Discarded in the process were the long-promised 10 mph (16 km/h) bumpers and airbags. The latter would have posed a great challenge; at the time, few off-the-shelf airbag systems were available and neither Lotus nor DMC had the resources to design and test their own.
Yeesh! That does sort of explain how the car was never quite one thing or the other, but a little bit of a rushed mix of ideas. Still, it looks cool in two chunks, right? I want to jam a seat, steering wheels and pedal box in there and go for a rip.