I work in the Salesforce ecosystem, happy to provide more insight. CRM did originally have a prospecting database, very similar to ZI, called Data.com. With GDPR laws (along with a few other changing trends), CRM didn’t feel they could continue offering a quality service, and shut down the service in 2018 to focus on their core competancy. In this same time, ZI thrived with the same industry challenges CRM faced.
When Data.com went bust, even Salesforce’s AEs were recommending ZoomInfo as a replacement to their own customers, as it can easily integrate back into a customer’s Salesforce instance.
So, CRM did try to copy it, but it failed.
I have to imagine that the other big guys are looking more at CRM’s failed experiment and seeing that as a warning for themselves rather than thinking they can outright copy ZI. I think it’s right to call that a moat.