Emphasizing sinkers to same-handed batters is one of the many quirks in the Rays pitching philosophy
When you think about what makes a good modern pitcher, there are probably a million thoughts that flood your mind. Velocity, pitch shape, sequencing, command, stamina, times through the order and exposure, the list goes on and on.
Some of these pitching concepts are very advanced, and require a multidisciplinary approach to understand. Even the smartest pitching minds are still working on them. But one of the most important parts of pitching is very simple to grasp, and maybe more importantly, is very easy for a player to change: pitch usage.