Each course has a limit to the number of points that you can earn toward your player level. If you continue to come in 1st place on the same course, eventually you will reach the point limit for that course, and your player level gauge will no longer increase when you race on that course.
Courses that have reached this limit will no longer add to your player level gauge even if they appear again in different cups or tours.
Note, however, that the R, T, and R/T versions of courses are each considered to be a separate course.
Race on as many different courses as you can to raise your player level higher and higher!