Because debian is a vanilla distro that does as little as possible, so it isn’t extra work to use it. Do you know what other distro tries to be as vanilla as possible. Arch. So if you just use the install wizard Debian and Arch are equal difficulty. AKA the easiest. Don’t buy the Ubuntu marketing hype. Just because someone labels themselves the easiest doesn’t mean it’s true. Just because another distro is labeled hard doesn’t mean it’s true.