A Linux distribution is a collection of software packages that live inside a repository. You can think of this kind of like an app store, that houses a bunch of different pieces of software for you to download if you want them.

Also like an app store, each piece of software in the repository is (hopefully) being developed and maintained to some degree by one or more software developers who are adding new features, fixing bugs, improving performance, etc. Some open source projects have decent budgets and many active developers, and change quickly, others are propped up by just one or two people and move a little slower.

Regardless… When one of pieces of software releases a new update, it is up to the distro maintainers to package it into the distro repository so that it can be downloaded by the users of the distro. Effectively this means that with each new version of a distro you’re going to get access to a smattering of new software releases that will both update the software on your system, and also make new versions of other software available to you on the repo side.

(Keep in mind that some distros, like Arch, use a rolling release model that upgrades things one at a time as they arrive, and other distros like Bluefin, use an atomic model which basically swaps out your entire OS each time you update. So they don’t ALL work like this.)

In other words, assuming your updating correctly, stuff is certainly changing each time you update to a new version. Those changes might be very noticeable (PopOS recently swapped out their entire desktop from Gnome to Cosmic!), somewhat subtle, or totally under-the-hood (like a Linux kernel/driver improvement). But they are happening.