Keep in mind that Western adult animation is rising, due to both shrinking populations and a vocal enough adult fanbase for animation that it’s the right opportunity to do it. The Internet may have also helped things, especially with stuff like Albino Black Sheep and Newgrounds.
A good number of animators working on such productions today may have started out in online animation. I’ve even perused Newgrounds at some point so I can see the movement taking off big time offline. There’s even a substantial enough number of adult cartoon fans not only in amateur activities also increasingly professionally employed at that.
Some of those working at channels like Cartoon Network and Nickelodeon were also animation fans themselves, bringing such sensibilities to the mainstream. It may not be a golden age as much as Western animation could compete with Chinese animation when it comes to replacing anime, should anime disappear.