They serve different purposes. One caches what we serve to the user, the other caches what we get from other tools.
I believe there will be cases where what we deliver to the user will change (different views of the same data set) but what we need to fetch from the tools will be the same. Especially depending on how we get data from those tools.

User -(cached)- Ployst -(requests_caching)- 3rd party tools

Eventually we may want to review how we fetch and cache 3rd party data so that we can have some of it pre-fetched in the background, not impacting response time to the user.