Interesting question.

One reason is that the OP already attempted a post-increment, and since the two increment types would produce the same outcome, why make the change?

Another reason is my personal preference for this counting situation. If, for example, I were on a sidewalk, tallying all the red cars that passed by, I wouldn't make a tally mark upon their approach (pre-increment), but rather after they crossed an imaginary line extending across the street from my position (post-increment).

Perhaps this ultimately boils down to personal preference, in cases like these...

I know its strongly favoured by many. I don't understand why.

My strong preference is to use pre-increment where possible so the increment operator is more easily seen (trailing stuff is more easily ignored). But maybe I'm missing something important about the post-increment?

A very minor consideration may be that the post-increment could be slower for some implementations that the pre-increment. The difference is so slight that it would be exceptionally unusual for that to be a consideration.

True laziness is hard work

In void context, Perl agrees with you:

$ perl -MO=Deparse -e '$x++'
++$x;
[download]

لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ