They’re a business. Reducing their costs (while charging you a premium) is absolutely what they do.

Apple’s whole deal for decades now has been building a vertical supply chain. Using their own SSD controller is one less component they have to pay others for.

They just don’t give a shit about downsides: aftermarket repairers or user upgradeability.

It’s more cost effective to integrate the controller.

Being worse for customers is just a happy accident.

It’s replaceable, it’s not upgradable.

Apple doesn’t use standard NVMe M.2 drives. The controller is built into the SoC rather than being on the storage device itself.

Hotmail ran on FreeBSD when Microsoft acquired the company in 1997. They started the transition a few years later and it was entirely hosted on Windows by 2005.