I really don't understand the reasoning behind this.
As you can see from the terraria store page it doesn't have galaxy achievements. If you are interested about achievements I believe terraria has in-game achievements
It does indeed have in-game achievements, but my question is about why they're not also in Galaxy. For example, Pillars of Eternity 2: Deadfire has both achievements in game and in Galaxy, same thing goes for JYDGE. It just would've been easier to check achievements without a need to launch the game.