you're looking at one aspect in a negative light.

on the flip side to your argument, maybe op travels by train 8 hours a day (4 there 4 back) and they only have one of those tiny little trays as a desk. I'd rather do something unusually instead of doing nothing boringly.

besides, wth have you done that makes your shitty opinion valid in this context?

I wrote a 16 page term paper on a Note 1 on a train while going back and forth to school. I also wrote some crappy android apps on the same phone for school. all on a crappy bluetooth keyboard and a 5.3inch screen. I think that gives me some idea of why such a thing exists.

want to know why I did it?

because:

1. I could and so I did
2. I had to because I was broke af in college and didn't have a device at home that could do half the shit my phone could
3. I had the time on the train so why not use it

so, to put it bluntly, I think it's pretty fucking applicable here.