From a design and manufacturing point of view you want everything to be identical. Differences are expensive.

From a profit maximization standpoint you want identical phones that can't easily be sold across market borders. Usually that's done in software (e.g. region locked video games), but that can usually be cracked, so a single design difference is the best solution. A great example is Nintendo's cartridge slot shapes that were different in each region despite the hardware being the same.

Apple had lightning everywhere; they were forced to change to USB-C. Therefore they changed to USB-C everywhere. The market protection design change remains the sim slot.

Imagine the shit show of trying to win support of third parties when you can't even standardize on one connector for the same device.