I have a question. Noticed that some of the apps have this:
... while other apps have this instead.

... so the question being, what does the "rebuild" do? and why do some have it and some don't?
I have a question. Noticed that some of the apps have this:

Look at the documentation for the App. It's likely different for each case.
some apps come with pre-built - ready to be consumed images, while others are build at runtime from sourcecode, so no remote image is involved.
rebuild might probabaly take more time vs image based ones
Hmm OK so this makes sense.