SMS is also super low level, it’s like the equivalent of ping. The GSM protocol already had a way to send small packets of data to phones for diagnostic/control purposes and someone figured you could also cram small text messages in there and thus SMS was born. It was really created as a way to monitize functionality that already needed to exist on the network for technical reasons. Back in the early days of GSM text messaging plans were a big money maker for the carriers because it cost them almost nothing to send SMS across the network but they charged customers by the message.