The question is, was it rock solid with few features? I don't know if it was this article I saw earlier but seeing how Salesforce has a lot of customizability and a Visual builder and maybe much of it was vaporware initially but maybe they simply scratched the right annoyances the customers had by providing features for that quickly enough.
Seen some ERP's for mid-sized customers and the good ones makes it easy to build views and otherwise customize the software up to a point for non-engineers. The code is shit but they've also produced a lot of things needed internally that we wouldn't have gotten done quickly enough by doing it manually.
https://retool.com/blog/salesforce-for-engineers