Is this a trend? A few minutes at Duotrope will show you how many magazines have response times of 180, 270, 360 days. Many of those magazines actually “require” a no-simultaneous submissions policy. The story is worse for presses. Most don’t take unagented submissions, of course, but those that do take 6 or 12 or 18 months to reply.
I don’t blame these folks much. I assume that editors, agents, and others who manage the channel are drowning in unsuitable submissions.
But how does the math work? Dune, Harry Potter, The Forever War, nearly any decent book you can think of took 15 or 20 or more submissions before being picked up. If those were serial submissions under a no-simultaneous submissions policy, that would mean about 15 or 20 or more years, plus 2 years for production, until those books appeared on shelves.
Generally presses don’t have a no simsubs policy. But mags do. And I’ve had stories that were well reviewed after they appeared, but that took three or four or five submissions before they were accepted. So must such works now take 3-5 years to find a home?