Well with all due respect I think you answered your own question. It is a timesink and shuold be monetized somehow.
As for the second part of your post: because capitalism works. Paying ad hoc for scenarios once in a while is not very efficient and an admission of defeat, so to speak. I have thought about this, and I'm certain that creating a marketplace around scenario creation would help heighten interest and productivity among the community.
Put it this way: you have to do *something* at this point. As you mentioned yourself elsewhere this week, scenario output has decreased steadily over the years.
At this point a small 'quarteron' of generals on the forum (get the reference? ) have the say-so over what constitutes a good scenario around here and that scares some people off. I saw fx the reception Matsimus received here because he had the audacity to make videos that weren't true to some tactical doctrine of the 1990's or whatever. Him not making SB videos anymore is a great loss.
I personally would prefer the way of Combat Mission: smaller, tactical vignettes with interesting head scratchers or smaller immersive scenarios with storyline.
Very few people can handle the battalion+ mega scenarios.
On the other hand, one thing SB can do, that CM cannot: big battles over many kilometres. I really like what guys like @ssidiver and @Apocalypse 31 are doing: Bigger or smaller battles where the player only control part of them. Very dramatic and immersive. And very important: beautiful maps with a sense of detail (atmosphere, the feeling people might live there).
But there is room for everything. Let the marketplace speak
Hope this makes sense. Everything I say come from a place of affection for the game