These are all titles skirting the line of cancellation in terms of sales. They haven't been canceled yet, but may do so anytime soon.
Blue Beetle: Under John Rogers this was one of the best superhero comics coming out. Now, not so much. Its decent, but there are a lot of decent titles out there. And neither Will Pfeifer or Matt Sturges have shown any ability to drive sales up.
Checkmate: Its now got Bruce Jones on writing duties. Yeah, that shows a lot of confidence in the title, DC.
Simon Dark: This is pretty solidly written by Steve Niles, and Scott Hampton's pencils add so much to it. Maybe DC's hoping that Niles' horror fans will buy the trades. Or maybe they are just going to cancel it.
Manhunter: Yeah, its just returned. And yeah, its as good as ever. But two cancellations in the past don't exactly inspire confidence.