Sure, it's easier to use a tablet while standing, but that's what I use my phone for, and it's always with me in my pocket. If I'm going to carry a 13" tablet around it might as well be a laptop which is thinner and lighter than a tablet + keyboard case.
Then there is always something annoying that I can't do on an iPad so I have to grab a real computer to do it.
I tried using iPads many times over the years but ended up selling them because a laptop + smartphone does everything I need better.