It’s completely arbitrary, and people at the time it became standard were very aware of this. Before, each country had its own prime meridian centered on its capital. In 20,000 Leagues Under the Sea, Prof. Aronnax tries to find out Captain Nemo’s country of origin by getting him to specify which meridian he uses. I can’t remember how Nemo avoided this, I think it was by using the American prime meridian centered on DC, when it’s very obvious Nemo isn’t American.

spoilers for a 150-year-old novel

Nemo is Indian, BTW.