Nah, they only need to split production lines when things are radically different. Excluding parts is usually easy, because the production line simply doesn’t install the missing part. The car still moves through the same line at the same rate regardless, so it saves them parts to not install.

The real reason they include them is so they can have their salespeople upsell you at the store. You weren’t originally planning on getting heated seats, but it’s only a few hundred more to do it and you’re already applying for the loan. A few hundred won’t make a huge difference. Also, we have this other feature that’s also only a few hundred more, and this other feature, and… Before you know it, they’ve upsold you into paying $5k more than you intended, simply by activating things that the car already had installed.