I've never seen anyone hold a tablet in landscape mode to use it while standing or walking.
I've seen someone, in some commercials, hold a tablet in landscape mode while stationary and pretend to write on it with a pen, but it was precisely an advertisement, not real life.
And I'm sure that you too are currently responding from your non-brandishable tablets sitting in an armchair, on the couch or even at a desk with a keyboard and mouse.
And guess what, that's the use you make of a computer.
More than %90 of my use of my iPad Pro is in landscape mode.