There’s been a few posts like this on various forums over the last few years, and I’ve had a similar experience moving more to headphone listening this year ... too lazy to pop upstairs to grab a head amp or dac and had a lovely old time listening directly from my iPhone into Shure cans.
That said, is ‘cheap’ the right word to use here? iPhones and iPads are actually pretty expensive, and that’s even factoring in the mass manufacture. Huge, huge investment goes into the R&D - hundreds of millions of pounds more then would ever be committed to a Hifi project, and the dac chips per se are household names in Hifi circles ... wolfson, cirrus etc. Imagine how much say, Naim, would have to justify charging for an iPhone 11! It’s a moot point, they just couldn’t design it.
So maybe we shouldn’t be so surprised when these devices actually sound pretty darn good. They aren’t hifi products, sure, but super-designed state of the art electronics made by some of the biggest companies in the world.
Looking at it like that and spinning the OP on its head for a moment - I guess we should actually be more surprised if we plugged them in and they sounded crap! 😁