Debian is more bare bones then Ubuntu, that’s why. Ubuntu comes with a lot of packages already installed by default. In Debian you have to install a lot of that stuff manually. You might also have to edit some configs for example. It’s not that hard, but maybe a little too much for a beginner.
I upgraded Debian to 12 last night, which required manually updating the source.list for the apt repos for example. It’s been a while but I’m pretty sure Ubuntu gives you a UI for upgrades? Upgrading Debian was simple for a techie who’s played around in Linux already, but it could be more intimidating for a newbie.