I remember when I was very little, in the 80s, action was pretty dominant in cartoons, there was stuff like Jason and the Wheeled Warriors, Thunder Cats, He-Man, you know, toy-selling vehicles, but we also had a lot of toy-selling cartoons for girls like Care Bears or My Little Pony. In the 90s, as a tomboy I was big into Teenage Mutant Hero Turtles (in the UK, they were hero turtles, not ninja turtles because people thought "ninja" sounded too violent), but I still remember that the biggest cartoons during that decade were things like Rugrats (Rugrats was HUGE), Hey Arnold!, Recess etc.
So... speaking as somebody who has always loved action stuff and who draws a comic in the action genre... are you sure there's really less these days, or is it the case that when you look back on the past, you only remember the shows you liked, and due to the truncated effect of looking back, you're comparing a whole decade-worth of cartoons with the last few years?
Because when I think of action/superhero/adventure type shows for kids in recent years, I'm thinking: Legend of Korra, She-Ra, Marvel Rising, Voltron, Adventure Time, Carmen Sandiego, Steven Universe, The Dragon Prince, Miraculous Ladybug, Spider-man etc. I don't really feel like there's a lower percentage of kids stuff, and in fact while doing market research at my day job I saw statistics suggesting that "adventure" is currently the second biggest genre category for kids entertainment, beaten out only by "comedy."
Also like.... the most popular movies for like the last 10 years have been dominated by action superheroes. Action seems pretty popular to me, honestly, people are complaining about how ubiquitous these superhero movies are.
It's true that on Tapas, action is a less popular genre than romance/BL, and yeah, that means my comic has grown slower than if maybe I'd done something in those genres, but I'm really not struggling that badly. There are a surprising number of Tapas Premium comics that have Action as their main or a secondary genre (for example, The Witch's Throne, obviously, but comics with a lot of action not in that genre include Magical Boy and The Beginning After the End). Action shows and comics now are a lot more nuanced than when I was a kid. Like they tend to have more complex characters and plot, and might have episodes with little-to-no action that explore why the characters fight. That's great for me because it's not only the kind of content I like to consume, but the kind I want to make.