That is essentially what the kernel cache is. Caches are pretty heavily customized for the database design because they control so much of the runtime behavior

That is essentially what the kernel cache is. Caches are pretty heavily customized for the database design because they control so much of the runtime behavior of the entire system. The implementations are different based on the software architecture (e.g. thread-per-core versus multi-threaded), storage model, target workload, scale-up versus scale-out, etc. The "custom buffer pool" isn't just a cache, it is also a high-performance concurrent I/O scheduler since it is responsible for cache replacement. Even if you were only targeting a single software architecture and storage model, it would require a very elaborate C++ metaprogramming library to come close to generating an optimized-for-purpose cache implementation. Not worth the effort. The internals are pretty modular and easy to hack on even in sophisticated implementations. In practice, it is often simpler to take components from existing implementations and do some custom assembly and tweaking to match the design objective. In either case, you still have to understand how and why the internals do what they do to know how to effect the desired code behavior. For people that have a lot of experience doing it, the process of writing yet another one from scratch is pretty mechanical.