An excellent and accurate summary of why no "one size fits all"
instructions are possible. I would only add that most of this applies
equally to Windows. The only reason it is seen as "easy" is that it comes
pre-installed!

Installing Ubuntu is not difficult. The steps are easy to understand and
clearly explained as you go. Once the novice understand that it needs a
minimum of two partitions, root (big, 20+ GB) and swap (tiny, ~2 GB) the
rest is easy.

With no licensing issues to worry about (every copy from the Ubuntu website
is "genuine Ubuntu") re-installing is hassle free if you don't like the
results the first time.