I agree, technology has innovated and then merged many tools into one, over and over, year after year.
Convenience is a huge part of that. A few devices can now competently cover the utility of what used to take more than a dozen devices. It saves production costs, storage space, use time, etc.
Nowadays, I use a phone for way more than calling a friend, its a boom box, a camera, a calculator, a clock, a calendar, a grocery list, a map, a voice recorder, a timer, a text messenger, a web browser, etc. all-in-one device.
I save money by only having to buy 1 thing that does many things competently, and it is so easy to have regularly at hand (or in pocket) since it is so small.
Convenience, Convenience, Convenience.
That said, I do not use my phone for all things, because it is NOT proficient enough for certain tasks. i.e. I use my laptop for photo editing, video editing, text editing, etc. because all of that is easier to do on a laptop, thanks to the interface, file management, user inputs, etc. that are all better tailored to those kinds of tasks.
I also use the laptop to watch movies with my roommate since we can watch it in any room, and it is large enough for both of us to view while lounging comfortably.
And that is another thing, COMFORT.
Laying around while using a phone is fairly comfortable, laying around while using a laptop can get uncomfortable after a short while because of how the laptop has to sit on something while in use, and how the hands must be to use they keyboard and trackpad.
The Nintendo Switch however has a magical accessory cherished by a pantheon of adorable snuggle goddesses…

Comfort extraordinaire!!!
And, it is still fairly comfy using in handheld or docked mode.
If they ever invent a more comfortable laptop, I will be so so extra happy! :D