Well, I'm also really new in the Linux world but as far as I know it is basically like android and different smartphone producers (Samsung, Sony, Huawei, LG, etc). So everyone has the same ground OS but adds different things or tools to it, e.g. different skins or user interface (for the Linux Desktop OS) or enchants commands like 'useradd' to 'adduser' with many new options and a better "interface" (just an example for ubuntu).
Maybe they are also doing some ground stuff different like partition management.
Or I'm absolutely wrong and there are huge difference between all of them.
So... I'm pretty sure the "hardcore Linux user" here will tell us