For sure. My guess is that the slush pile count is exclusively of unsolicited, unfamiliar authors. Someone they've published before probably skips the pile.
I think they might be publishing stuff their core audience really likes, btw. It's just that audience is probably a niche.
I think this is an ongoing challenge. You see it with comics as well, where Marvel and DC have gotten really good at knowing what sells to their niche audience. But their audience has been in lengthy decline, in part because they've focused on selling to their niche audience rather than figuring out how to broaden their base.
I think they might be publishing stuff their core audience really likes, btw. It's just that audience is probably a niche.