I think that maybe if you devode to one genre of music it makes some things easier for you.
Each kind of music has it "tricks" of how it is played,so if you learn many songs of the same genre,when you encounter the same rythm,chord progression or the way triplets are played in that genre, your fingers and mind are allready familiar with them.
Furthermore the professional musicians have to make a living by their job so if they play lets say in a jazz club they have to be good at playing jazz and they focus on their job.
Or a professional musician who plays folklor music for specific bars of that genre and for weddings.
I am just an amateur and I will agree with you that if there is no variety in music you are playing you are missing a lot of great music that there is out there
(and a lot of great styles/voices that there are in there
)
But if someone feels good by playing just one kind of music I can understand that.