Hehe I was thinking about FCA/Stellantis vehicles when I wrote that. I know it works and there are components made to work in that environment but it always felt intuitively wrong to me. Especially when the other side of the firewall is a much better environment and not far away

It’s because when placed inside the engine bay, the large wiring harness is shorter, which is not only cheaper, but also shorter wiring helps with the consistency of electrical timing and reduces noise.