That's not true. Plenty of Discord communities have dozens of channels with long-running post histories, pictures, FAQ content, beginner guides; server roles and titles, permissions, custom emoji, stickers, etc.
Migrating all of that stuff to a new service (which may not even support it all) would be a huge pain.
Migrating all of that stuff to a new service (which may not even support it all) would be a huge pain.