There are so many decisions other than just the dates that you implicitly make (or are made for you when you book your flight). Do you want insurance? Wi-Fi? Extra leg room? Turbo prop aircraft? Jets only? 2-3-2 seating? 3-3 seating?

Logically, you should want to control each of these variables while searching for flights. If you are ready to trust a flight aggregator with these choices, some fuzziness in price seems acceptable too.

You are probably thinking that you don’t want to make a choice about aircraft type or seating configuration and so, whatever the search engine shows in whatever order is fine by you. If so, consider that others might have the same ambivalence towards price fuzziness.