My *blind guess* it that originally, in TP descending parser FSM, it was just simpler to copy-paste {/} and (*/*) pairs verbatim, than making special cases of "one closing another"
you meet '{' - search for the next '}'
you meet '(*' - search for the next '*)'
it is simple and large;y error-safe, just colling one single search fuinciton, Pos :-)
REP SCANSB is all you need, well, almost
multivariant searcher is much more complex, and thus slow and error prone.
This, by accident, enabled nested comments. "And programemrs saw it, and they saw it was good" and demanded it to forever be so :-)