because SMS has inherent costs in some countries, because SMSs are tiny (I'm pretty sure his example json structure was larger than a SMS max size even), there is already a mechanism in place (to see all SMSes), which would have to be hijacked (to not display what would be practically garbage to the end user)

push notifications already existed 3 years as a thing before this talk

Whatsapp, twitter, etc, all existed before this talk as mobile services (and twitter via a SMS interface, which is the far more reasonable way of using SMS uniformly across all phones)

It was a talk 3 years too late, data plans already existed, push services already existed, implementing such a thing via SMS would only lead a company to get ~6 months max use, wouldn't be as easy as other methods (receiving a push / making a web request, vs receiving a possibly fragmented SMS, and then having multiplatform hiding of this message), etc etc etc. I personally have to wonder if the talk was comedic (the part about how app stores make it impossible for people to find your app, makes me wonder this as well)