Of course, there's also the fact that extra ports take up more space, and it's easier to just eliminate features that not enough customers care about. But enough people seem to be complaining that it looks like it really is just cargo-cult behavior, just like these companies have needlessly aped Apple on other design decisions instead of trying to pursue other market niches.
Apple went exactly the other way and built a data port into it. And did the same thing with the Apple Watch (the prototypes had an extra set of contacts in the band slot that people were excited about). Disappointed.
Most people probably wouldn't really care for this, and the ones who do probably have portable media players already, so I would prefer to keep the headphone jack. The reality is, though, that USB-C appears to be the future.
Of course you'd still need two ports if you wanted to charge at the same time.
It would probably be more interesting to see smartphones that could use the headphone output as a digital signal, like a coaxial output. We want the 3.5mm output anyway, so why not just let it dump a digital signal to an external amp?
Mobile phones are thermally constrained these days anyway.
Would it hurt anyone to put two USB-C ports on a smartphone? Thank goodness my phone still has a 3.5mm jack, but some people would like to charge their phone and listen to (wired) audio without having to buy an adapter. And it's not like this is an uncommon use case either, anecdotally some of my friends with iPhones face this issue.