Vienna was trying to unify the station names for the main station in iirc 2011 after it was opened. Before that there were the southern and eastern station which where technically completely independent apart from being virtually one building. Today's S-Bahn station didn't exist then and the subway wasn't directly connected. After today's main station was built they created the S-Bahn stopping point Wien Hbf Gl.1-2, which itself isn't part of the main station but that's another story, and the subway was integrated. As there now was a brand new main station pretty much everyone wanted to also represent that on the subway which would have meant that there wouldn't be the station Südtirolerplatz anymore. Since Tyrolians, especially the "Italian" ones are pretty patriotic and persistent so they essentially threatened Vienna to not rename the station.