There is a good Adam Savage video on yt about the engineering of the thunderbolt or whatever cables.
They still should be shipped in bulk to the store but it makes more sense why they wouldn’t be given away free
iPhones don’t come with those expensive high-bandwidth cables, they come with charging cables that only do USB 2.0
I’ve had one apart and to be fair they are not carelessly made. They’re jacketed in soft silicone under the braid and have thicker than average stranded conductors. You can totally use whatever cables you want, but theirs are built a little better than you’d think and they just feel nice.
Maybe this is a tactile/autism thing for me?