The phrases 'all your eggs in one basket' and 'To be sure, to be sure' come to mind. Putting your archive content in two cloud platforms increases your chances of accessing content and generating revenue.
It is worth noting that using the biggest of public cloud providers does not mean your content will always be available. Fact. The big two recommend that you employ their redundant multi-region services to ensure that the lights stay on when regional outages occur. That of course incurs more cost as does the movement of data between those regions. Redundancy and business continuity require additional investment regardless of the archive platform, but it is clear that many small and medium organisations, those without the massive corporate deals, assume that public cloud means protected and always available. Sadly that is not the case, so deploying a multi-cloud strategy is becoming more important to ensure business access to the content you own is guaranteed.
As we all work from home more and more the requirement to self-serve access to content has become imperative for many industries. In the media industry, many business models need frequent and quick access to archive content in order to generate revenues so egress fee based models with varying performance SLAs are often prohibitive or inappropriate. But, the comfort of knowing monolithic, 'too big to fail', entities like Amazon or Microsoft have a copy of your archive can be alluring despite those limitations.