I think it is an image thing (pure speculation on my part).
Apple has left physical discs behind for a long time.
Keeping an application called DVD Player in the Applications folder would look dated.
On the other hand, removing it altogether would raise protests.
Since most people (most of the very few that use DVD discs in current Macs, that is) would never call DVD Player anyway, everything just works as before: you insert a video DVD and DVD Player takes care of it.
I bet that most people either don't care or never noticed that DVD Player is now "hidden away".