Why would people buy it on disk when it was released onto Disney+? It has other metrics of success - it was one of the most streamed programs in March 2022.
I can't speak for all kids, but for mine it's the opposite—the main TV remote they use controls our Fire TV Stick, and has a button for Disney+ built in. Plus, our iPads have Disney+ apps. Whereas our optical drive is a PS4, so they'd need to use the TV remote to switch to a different input, plus the PS4 controller. I'm not saying they couldn't figure it out if they wanted to, but for them, navigating menus to Disney+ is much easier.