What you say about the deeds makes sense. If this is the case, then it is indeed a non-issue because we just aren’t seeing that many sales.
However I think you are too quick to dismiss the importance of a property passing from weak hands (banks) to strong hands (investors who may keep them off the market for a while). This may or may not be happening, but if it were, it would not be a “non-issue.”
As to whether it is happening… I agree that there doesn’t seem to be evidence of it, but I don’t really know enough about the procedural aspects of bulk buying to have an opinion of my own.