A general survey builder gives you a new dataset every time you send a survey. Employee survey software gives you the same dataset with a new column, which is what makes trend lines, segment comparisons and the question that has not improved in three rounds possible at all.
The other differences are anonymity and org structure. HR platforms enforce a minimum group size for reporting, and they sync with your HRIS so results split by team, manager, tenure and location without you rebuilding a pivot table each round. Pricing models differ too: SurveyMonkey charges per survey creator, so cost does not scale with headcount, while HR platforms charge per employee. For a single one-off survey the general tool is the right call. From the second round onward it is not.