[api]

The big down-side is that they'd end up with really fat binaries and edge case bugs in some apps across architectures.

Apple can pivot architectures, but I don't think they do it lightly.

[brucehoult]

Modern MacOS and iOS app size is completely dominated by image and other media assets. The code is down in the noise.

[saagarjha]

This is not true; most popular iOS apps have very large binary sizes.