I used to see legit craigslist ads for SA, BA, and CA runs for ASM, Thor, Iron Man, SS, XMEN, FF, etc. Now all I see are dealer ads.
The 2 LCS near me used to see regular SA- BA collections walk through the door or phoned in from around the state at least once a month. It's been a year since they've pulled in a new collection.
I think it's a combination of both. There are fewer collections coming to market than before and the ones that are have more market aware owners who are either pricing out the smaller dealers or going directly to the top auction houses for the convenience.
Not sure if the scarcity has anything to do with there actually being less hidden collections or that people are quietly holding onto them.