There is several aspects:
1) Tagging the feature as name and thus not tagging the feature (here: sports=tennis was missing to define the feature)
1.1) Map renderer evaluate those features to colorize the area if the tennis court in a certain way. No sports=tennis tag, no nice colouring.
1.2) OSM is so much more than just a map. For instance, one can evaluate the area of a city used for buildings vs. the area used for sports facilities. That only works if you tag it correctly.
1.3) It is an international project. Names cannot be translated automatically (and even with KI I doubt they ever will, at least safely). sports=tennis on the other hand can be easily translated by simple software.

2) Entering something that is not the correct name
2.1) When you search for locations, the wrong name might pop up and will be missleading
2.2) You walk as "illiterate" European through a Chineese city looking for the gym <add some Chineese signs>. What would help you more? An OSM map with the <add some Chineese signs> that you can compare to the (non-latin) signs on the buildings? Or a text "really cool gym" that you cannot compare to <add some Chineese signs>?