To point out the difference and problems with becoming accustomed to horizontal vs. vertical - try writing something of significant length, in English, vertically.
Just do it.
See how weird it feels. See how much slower you are at writing, and how awkward it looks.
It isn`t that it is something incredibly *difficult* - it is that over time, you naturally make ways to connect letters/characters to speed your writing up. The way you finish one letter has an effect on how you begin the next. Even for people who write 100% in "print", there are some hints of a script style in some parts.
With reading, the brain likes to shift to sight reading - in other words, recognizing the pattern rather than actually *reading* everything manually. It is faster and more efficient... But only works when the pattern is the same. It doesn`t shift between horizontal and vertical well.
If you learn these script-like patterns for writing horizontally, and sight-reading for horizontal reading... they will only apply to things horizontal. Basically, you`ve just added another step to your learning that didn`t need to be there - and wasted some time on developing a skill that will rarely be used.
I mean, see how fast and relaxed you can read this - in English...
Code:
Arr
nee
dla
ad
hx
oet
wdh
i
fys
ao.
su
t
c
aa
nn
d
If you are used to reading horizontally, like I would imagine everyone is who reads and writes English... You likely felt very weird reading that.