I Think Empire is a bit different because they are in a more remote or unpopulated part of the universe or perhaps the best way to describe it is not colonized. And that is the difference.
I’d like to think that in the SW galaxy there are charted and uncharted systems.
Charted systems have a name as expected.
Every system has only one habitable planet or moon, so to make it simple they have the same name. It’s even logical.
And it does not matter colonized or not.
More remote parts of the galaxy are uncharted and have no name. No system no planet no nothing.
Simple.
The planets in Star Wars and Rotj apart from Dagobah planet or system whichever you prefer are all known and Chartered and colonized.
Dagobah is charted, but it’s been erased from the charts, so it exists, and was given a name, only very few know about.
Anyway it is a bit strange that a whole system is named after a single planet it’s not confusing but it would be like calling our Solar system Earth System.
Not more strange than the sound travels in space. And even that can be explained with a unique Star Wars galaxy particle, that is present in space.
Star Wars is a sci-fi fantasy, but even in not fantasy sci-fi, like the Asimov’s Foundation universe, in a huge galaxy, with thousands of planets, I could imagine calling the Solar system simply Earth system.