I wonder if the use of CGI is part of why this is the case. I love it, don't get me wrong, but when a rescue mission to an asteroid takes months of VFX work because they're swooping through swirling clouds of gas it can make episodes take longer. Heck, even the views out of the windows on SNW are masterpieces instead of christmas lights in front of a black curtain.
With older shows they had the sets and costumes built, so filming a walk-and-talk or courtroom episode wasn't as big of a technical lift. Then there was the desire of just about every show to reach 100 episodes, which meant they could get that sweet, sweet syndication money.