It's kind of confusing because back ten or twenty years ago that wasn't really the case. They were way more different, architected entire processes different, and were more disjointed messes with way more pros and cons different between them. That's where a lot of the distro hopping and distro wars you might hear about stem from. It was harder to change them to mimic each other.

There's some more subtle differences like some distros choose to hold back updates until they've been tested and some push them out ASAP, immutable vs not immutable. But for the most part, problems you might come across from the distro itself causing you to need to move instead of just pulling in a package are much less now.