When we call marketo a marketing automation tool and are not able to send the SMS from marketo (without using third party tool integration), I feel something missing.
I view it as being similar to email. They have brought email into the platform because it's a mainstream form of communication with customers/leads and I am perceiving SMS to be the same as we move more and more towards a mobile centered world.
I agree with Kevin on this. Recently Salesforce marketo cloud have added a feature, we can create/manage digital campaigns (fb,insta etc) within the toll itself and I feel it's a great move. We have to upgrade ourself as per the market need and customer behaviour.
Managing FB and Instagram campaigns using their public APIs is so different from SMS, it isn't even close to a valid comparison.
There are technical leaders in the SMS space (Twilio in the US, others abroad) and there is no way Marketo will ever, ever build a best-of-breed SMS service to compete with people who have built and tuned their infrastructure for ~20 years.
In addition, the compliance rules are very diff for SMS vs. Email. And Marketo has barely enabled permission mgmt now that it's a big deal with GDPR. The number of Firms using SMS is very small in B2B. Doesn't seem like a core component unlike email which 100% of people use.