Btw I never understood the reason for imessage being so popular in the US I remember in France when it was introduced, most phone plans had free SMS, but data

Btw I never understood the reason for imessage being so popular in the US I remember in France when it was introduced, most phone plans had free SMS, but data was paid (and expensive), so people around me would disable it on their iphones How come that effect didn't happen in the US?