Many - almost all - great composers have been also good performers. Bach, Mozart, Beethoven, Chopin, Debussy, Ravel, Prokofiev, Bartok - just to mention the very famous ones.
Nowadays you are either a composer or a musician - both together is suspicious: either you are a good composer but not a good performer or vice versa - so the prejudice of many people.
Why are 99% of the pieces played - let's say piano recitals - from composers who had been also pianists? - First of all it's great music, but more and more important is that you can enjoy playing this pieces - it's fun! It's pianistic and the movements of the hands are organic. That means not necessarily that they are easy and simple pieces, no - most of them are extremely difficult - but if your fingers get used to that it starts to be joy.
If a piece is not pianistic, guitaristic, xy-ic, then it will be not played very often and probably never after 100 years. Composers: touch the instruments again!
