Because they bought an entire company to do it with, because the value proposition of doing that was better than continuing to pay the Qualcomm tax, or conversely siding with Samsung to bring Exynos LTE to the US (and they already have too much of a complex relationship with Samsung; to the point that even on the iPhone 8 and X, if you bought an iPhone instead of a Galaxy S, Samsung still makes a profit).

As in: they earn more if an iPhone X is bought than if a S8 is bought? If not, do you know the relative size of the profit?

Not more, afaik, although some headlines seem to have reported it. All I know is Samsung is happy no matter if you buy an S8 or an X.

It is a part of their core product differentiation. They can get better performance and longer battery life by owning the hardware design and OS design and being good at it.

Apple in particular understood lomg before competitors that battery life is an extremely important real world metric. Doing their own SOC helps them optimise that.

Seems like revisionism to me? Before the iPhone/smartphones in general, battery life on a mobile phone of a week was not uncommon. One of the first criticisms of the iPhone was that you had to charge it every night. I'm not sure I'd say that they had some unique insight into the importance of battery life.

Not revisionism. Prior to the launch of the iPhone, "smartphones weren't very smart" to quote Steve Jobs.

Anyway, you are comparing the battery life of touch-based smartphones with its non-touch predecessor which isn't a fair comparison. Besides, mobile phones that could last for a week from a single charge are definitely not considered smartphones, those are feature phones.

Batteries are part of Tesla's core differentiation as well. Even if one might argue they make too much in house, taking batteries on seems like a reasonable move to me.

I think Blackberry cared a lot more, but it didn't work out well for them.

Well, I guess it's apparent now that it fell outside of my immediate observation. I would be curious what the risk calculus on that decision was. I think it still fits in to the same narrative that I was building though: Tesla seems like they want to bring everything in house while Apple has only brought one piece, the jewel of the system, in house.

I don't think Apple designing (not making, designing) their own SoC is comparable to Tesla making their own seats.

They don't make their own chips, though, do they? Or screens, or whatnot. Making their own SoC is like Tesla making their own drivetrain, not like making their own seats.

Perhaps that is their secret sauce?