It used to be easy: a company developed a new application, chose a database solution, launched the new application and then tuned the chosen database solution. A team of DBAs looked at the infrastructure as well as the workload and made changes (or suggestions) as needed. The application then stayed in production for years and small tweaks were made as needed.
Those days are long gone.
As technology has evolved, so has the workflow and deployment strategy within the large enterprise. Large, monolithic applications are being split into several microservices, generally decoupled but still working together and somewhat interdependent. Waterfall deployment strategies are replaced with agile methodology and continuous code deployment. Tuning and maintaining large installations of physical hardware has become less of the focus with the advent of virtualization, containerization, and orchestrated deployments.