Listen, SMS sucks (and by extension MMS which is what manages the media sending) but universality trumps all. It's a simple system that despite all its flaws is still available everywhere and used for everything. It's an "innate" technology. Being innate is a feature far more powerful that stickers and read receipts.

RCS is a great standard to replace it but SMS is so ingrained that it wouldn't be gone even with RCS on every phone and every operator interconnected.