Really hate the evolution of smartphones, I must say. First they take away the ability to swap out the battery (especially for high end devices), giving the phone a very predetermined life span. Anyone who's been using a phone for several years know that after a while, batteries tend to hold their charge shorter and shorter and eventually burn out completely. That's about the time the phone manufacturer thinks it's about damn time you bought a brand spanking new phone from them, rather than spending 10 or 20 bucks for a new battery.
Over the last decade, smartphones have evolved so immensely, that new features and upgrades in terms of performance and screen resolution really were a huge step up, even for the casual user. The same can't be stated quite as much today, where the already high definition handset screens of yesteryear are replaced with new models that offering even higher resolutions. Resolutions you might not even have on your big screen TV, or even at the movie theatre.
Shortly thereafter, we're seeing expandable memory become a thing of the past. You can argue all day that cloud storage and streaming is the future, making local storage less relevant. But I haven't seen that trend really lessening the need of storage. Apps get heavier in terms of data use, and higher resolution cameras continue to make even larger, more pixel-dense images. They still need to be stored somewhere.
What it all boils down to is commerce, really. Phone manufacturers don't like the idea of cheap SD cards, since it's a missed opportunity to charge extra for additional built-in flash memory. Because why would you shell up hundreds of dollars extra for additional onboard memory when you can just buy a 128 GB micro-SD card for 30 bucks?
ZDNET's Adrian Kingsley-Hughes puts it spot on here:
"Manufacturers can't charge a premium for an SD card slot, but they can charge a $100 for a few extra gigabytes of flash storage."
Even headphone jacks are omitted on some new ones, because some jackass thinks everyone should get crap bluetooth headsets instead of proper cans with some decent sound.