Yeah, there are some really good "Mosaics". And, it is a crime that the people responsible for them are not being given professional work.
But, there is also a fair amount of crap. Strike that. There is more than a fair amount of crap in the "Mosaic" project.
And, there is a difference between telling a story and telling a worthwhile story. Give me an hour, and I could give you a page-length story without typos. (Yes, me without typos.) But, that story would not likely be worth reading.
Telling a worthwhile story in a short ranger of pages is difficult and few, if any, writers can do that consistently. And, people who can do that can usually use the same skill-sets to find better (paying) work elsewhere, so they are not going to bother with writing fiction to pay the bills.
That would, admittedly, be my preference. Detective Comics in the 90s often gave me a complete story every issue, and there's a lot of appeal in that approach. But it's rare these days.
That was a rare run of comics that was specifically set up to do that. And, while Grant's run on "Detective Comics" was arguably defining, not all of the stories were great unto themselves. And, come to think of it, there were more than a few 3 to 5 part arcs.
Dom
-and some stories simply cannot be told in one issue.