It's less cumbersome for them to write their content, yes. There's initial upfront effort, but their subjective experience of actually using the system to do what they want to do is better.

It's the same reason why people invest dozens or hundreds of hours in configuring their editor - yes, the defaults work fine, but you can make them work better for you. And yes, you're probably not going to make that time back... but if the actual experience of using it is better, it's still a net win for the author.