With SMS and MMS being dated and often not able to accommodate current needs they're still the only common texting protocol all the other services can still fall back on as common link between all the different competing standards. As appealing as RCS is, Apple has already stated it will not support it in iMessage so that alone is enough to pretty much table it as something to take the place of SMS/MMS. The texting environment already has numerous proprietary protocols (iMessage, WhatsApp, etc.) that their developer/maintainers refuse to share with other services so it's pretty much matter where we as consumers don't need yet one more standard that further fractures texting. Way too many people mistakenly assume texting has the same universal compatibility as email but it's very clearly does not. Sure it would be nice if some standard like RCS became the new default texting protocol, but with fellow texting platform heavy-weights like Apple and Facebook shunning RCS in favor of their own proprietary standards at best we as consumers just have to consider ourselves lucky that SMS/MMS is still viable despite their weaknesses.