The 'just a kids show' aspect is a big part of it, but not because of the perception... because that's what the budget was allocated for in the first place. With three or four other shows, Star Trek Prodigy wasn't supposed to move the needle on convincing Star Trek fans to sign up for Paramount+... it was supposed to get kids interested in the franchise. But the cancellation also isn't some condemnation of that idea or an acknowledgement that that idea was a failure... it's because the goals for kids TV change very quickly. This is basically what happened to Wing Commander Academy: being the highest rated show in your programming block doesn't matter when the network decides it isn't showing animation anymore. You won't convince the internet (man-ternet?) but the days of TV ratings deciding a show's fate ended twenty years ago.
In this case: back in 2019, Prodigy made a lot of sense for CBS: they were reinvigorating the Star Trek IP, kids superhero stuff was big, CG action shows were huge, there was a growing need for streaming shows (and investment to go with that) and so on. There were also huge relationship benefits: it would lock down a whole web of creatives, producers, artists, post production outfits, etc. that Paramount wanted to be tied to. In 2024, though, streaming is now the whipping boy for the declining movie industry and budgets for streaming content are getting smaller and smaller. And Paramount is more for sale than ever! Which means that long term relationships don't matter so much as showing that they're working to make money in the short term. So a show that they think will pay off for the core IP in five years isn't so appealing on the balance sheet... and of course the types of kids properties that were hot when Prodigy started naturally aren't anymore, CG action shows are way down and so is stuff produced in North America in the first place. 'This is breaking even but it means we have six animation studios working for us and ready for the next thing!' isn't appealing now that they don't want those animation studios for anything else. And so on, it's a zillion complex things.
Is there a world where Prodigy came out and it was as big as Bluey? Sure, and in that timeline they probably wouldn't have cancelled it... but it's important to understand nobody made the show in the first place believing that would happen, either.