Why is the watch item designed as one time use only, versus QSS is multi-use.
The repeat use feature of QSS basically destroys certain champs abilities early game whereas Zhonya must be a full item to get repeat use out of it.
QSS severely adversely effects Malzahar's game play.
One "work around" would be to covert Malz suppress to a knock up. At least that way, QSS effects would be mitigated.