If you ask many companies they may not think about their data being multi-cloud. The thinking is more about their application estate.
On pressing you will be told that they may have windows filers, have a NAS or SAN, perhaps are using object storage either on-premises or on-cloud with something like Amazon S3, use email, perhaps outsourced to someone like Google, which also provide their employees with a cloud drive, are using a cloud based CRM such as Salesforce and perhaps a raft of other cloud based Apps that have file storing capabilities.
Congratulations, that is what a multi-cloud data company looks like in 2019 !
The great thing about API’s is that developers can create brand new apps that tap into an ecosystem of web services. This is especially true of data based services (after all if data is the new oil etc etc !). Why store your own proprietary App data when there are so many great data stores out there ? In fact why not make data key to your app proposition ?