The org chart makes it look tidy. Marketing generates demand, sales closes it, customer success keeps it. Clean handoffs, clear ownership. Then renewals slip, expansion stalls, and everyone turns and looks at CS.
But CS is usually two or three people covering hundreds of accounts. They are doing triage. They talk to the customers who raise a hand and the accounts flagged as at risk. Everyone else gets a quarterly check-in email and then silence.
That silence is a marketing problem
It is a marketing problem because marketing is the one function that knows how to communicate at scale with people who have not asked. Think about what your existing customers actually receive from you. Release notes, if you write them. A newsletter they were auto-subscribed to that was really built for prospects. Now and then a webinar invitation about a problem they already solved a year ago when they bought.
Almost nothing that helps them get more out of what they already have. Almost nothing telling them the second module exists, and why the customers most like them added it.
That is a strange thing to leave on the table. Expansion revenue is cheaper than new logos, it moves faster, and it closes at rates acquisition cannot touch. It also protects renewal, because a customer using three parts of the product does not leave the way one clinging to a single feature does.
So what actually belongs to marketing
Quite a lot of it, once you look. Onboarding sequences that get a new customer to first value. Adoption content aimed at the users who never showed up to training. Communication segmented by which features an account actually uses. Case studies written for existing customers rather than prospects, showing them what the next step looks like.
None of this needs a new team. It needs a decision that the marketing function does not end at the contract.
The reason it usually does not happen is measurement. Marketing is judged on pipeline created, so every hour spent on an existing customer is an hour that never shows up in that number. Fix the measurement and the work follows. Leave it alone, and you will keep buying new customers to replace the ones nobody was talking to.