It's not only because of the obvious reason - to get better at playing the organ.
If organ playing is your calling, you need to practice it daily because you need to have daily ideas and experiences which you should write down and share.
Writing down your organ playing experiences is the only way you can make sense of complex things that are going on in your mind.
Sharing those experiences with the world enables you to grow your fan base, get feedback and be in tune with the rest of the organ world.
If you don't believe me, just skip organ practice for a week or more and see what happens.
What happens with your relationship with yourself, the people around you and the environment.
Besides all those artistic reasons, organ playing also has a biological function to us.
It's part of our survival mechanism.