Why Debian requires manual edit of /etc/apt/source.list to receive LTS updates?

Question

Why in Debian, you must manually edit your /etc/apt/source.list in order to receive LTS updates as explained in the official Debian LTS Wiki?

Why it's not like Ubuntu where LTS updates arrive without the need of this manual change on /etc/apt/source.list?

this is the an original /etc/apt/source.list after the install

deb http://deb.debian.org/debian buster main
deb-src http://deb.debian.org/debian buster main

deb http://deb.debian.org/debian-security buster/updates main
deb-src http://deb.debian.org/debian-security buster/updates main

# buster-updates, previously known as 'volatile'
deb http://deb.debian.org/debian buster-updates main
deb-src http://deb.debian.org/debian buster-updates main

and this is the one from official Debian LTS Wiki

deb http://deb.debian.org/debian/ buster main contrib non-free
deb-src http://deb.debian.org/debian/ buster main contrib non-free

deb http://security.debian.org/ buster/updates main contrib non-free
deb-src http://security.debian.org/ buster/updates main contrib non-free

Answer 1

Debian LTS doesn’t require editing sources.list. The differences in your examples are the added contrib and non-free sections, which are only needed if you require packages from those sections; in such cases, sources.list would already contain the relevant entries. They are not enabled by default, which is why your post-installation sources.list file doesn’t contain them.