Maybe this is true for some regions, but in general the reason was money. SMS costs money, Whatsapp intially had a low one time or annual fee that was way below what you used to pay for a few SMS, but you got better service than MMS for that fee. And now it’s free and sustained by network effects.
Mea culpa, aber ich auch nicht die Sprachpolizei, ich mach mich nur über die CDU lustig, wie sie versuchen Sprachpolizei zu spielen.