Learning isn't all fun. Everyone thinks they can make learning fun, but it's always a combination of things that are very specific to the person suggesting it ('Actually making everything Thomas the Tank Engine themed is magic and works very well!') or just wistful thinking ('If the teacher didn't tell me to work I would have been more motivated!'). And most of the more valid research suggests more conservative approaches work pretty well.

Schools have to make kids do stuff that just isn't fun, without paying them or offering any real incentives (other than grades, which only count in the last year), so they need to make sure kids don't have excuses to shirk.