Maybe I’m being too narrowly focused here, but I think Urtuk looks distinctly different than Darkest Dungeon. A core part of DD’s art style is posing. The actual rigged animations are pretty minor and clearly just a way to get from super-awesome pose to super-awesome pose. Urtuk put a lot of effort into their rigged animations and don’t seem that focused on posing at all. This makes DD feel like you’re playing in a comic book, whereas Urtuk feels like a video game. Though Urtuk does have a pretty similar core style, the animation looks pretty different.
I think this style’s popularity happened as much for technical reasons like @Nightgaunt said. A tool like Spine is a good example. It’s gotten way easier to take a carefully illustrated static 2D image, rig it and then animate it in the last 5 years. You can go straight from concept art to game and have it look pretty good. You don’t need to build a style that’s easy to draw dozens of times to create 2D animations. It’s like how Flash games all had a similar vibe back in the day.