I am aware of the difference between using
$...$ (in moving arguments, for example), and yes, I've read the answers to this question: Are \( and \) preferable to $?). I also know the definition of
(taken from Section 55.2 of source2e.pdf)
My question here is: couldn't
\) have been defined as robust commands in the LaTeX kernel? Is there any (non trivial) reason explaining why they were defined as fragile commands?