we seem to be seeing less and less of the main characters now as we have six 6 divisions of main characters:
That's because they don't have to pay them for that episode. No name characters mean cheap episode.
Generally, series regulars (main cast) are paid for all episodes, even ones that they don't appear in. It's pretty much the industry standard in contracts.
'Guest Stars', or recurring cast are only paid for episodes they film.
