Without internal Twitter context, but having seen companies with marketing teams... there's a lot of people involved in doing close work with partners, whether advertisement ones or others. On the tech side it's kind of like AWS support - sure, everyone had access to the support portal, but once you start spending $$$, you'll get dedicated people sitting in your company's slack channel, providing support, advice and planning if you need it. (Sure, it doesn't always work great, but the idea holds) I'm sure that whoever was the big ad spender with Twitter has a dedicated contact reachable more directly. (And possibly negotiating better deals than advertised to everyone)