With the current trend of ever-shrinking tech devices, we have seen an explosion in the abundance of portable electronics. Fifteen years ago Apple launched the iPod, a device so foreign to people that Steve Jobs had to explain you could legally transfer your CD collection to your computer then onto your iPod. Now it is expected that the little (or big) phone in your pocket works as well as any desktop computer with fully developed applications and lasts a full day on one charge. There are many different advances that made this possible, such as the reduction in size of the fabrication nodes, increased battery storage, and much better video display options. But I think one change in design philosophy in particular has driven the current trend in tech.
Due to portability requirements phones have become a microcosm of the tech industry, specifically in the trend of increasing complexity at the cost of repairability. When the first iPhone came out there was no option to change battery or storage configuration, options both available on competitors’ devices. And yet people flocked in droves to Apple’s simpler, less-customizable devices, so much so that now Google produces its own phone, the Pixel, which has a non-removable battery and lacks a microSD slot. Logic dictates that there must be an outside pressure to force a competitor to drop a substantial differentiator from other products on the market; I would argue that factor is thinness.
The size of an SD card slot seems pretty inconsequential on a device the size of a desktop computer but when it takes up 1% of the total space of a device, there are arguments for much better uses of the space. A better cooling system, larger internal battery, or just space for a larger PCB are all uses for the extra space that may make the device better than it could have been with the SD card slot. When you look at the logic boards for the iPhone, this point is illustrated; there is just no space for any extra components. 
Driven by space-saving concerns, complexity increases as smaller and smaller traces are used on the PCB and components have to shrink, shuffle or be removed. Proof of this is in the design of larger machines such as the Macbook, a 12-inch laptop with a logic board smaller than its touchpad, which features a mobile CPU and no removable storage.
Demand for ultra-portability has led to devices that are so small that they are almost impossible to repair or upgrade. However, this trend cannot continue indefinitely. Moore’s law has taken a couple hits in the past couple years as Intel struggles to keep pace with it and PCB manufacturing can only get so small before it is impossible to fit all the components on it. As size becomes less of a differentiator and reaches its physical limits, tech companies will have to look to new innovations to stay relevant, such as increasing battery life or designing new functions for the devices.