There were 12 Golden Calves not one

 Rav Yakov Kaminetsky (Emes L’Yakov Shemos 35:1): The sin of the Golden Calf was the opposite of the Giving of the Torah. Because our Sages said that at the Giving of the Torah the Jews were totally united. In contrast the Yerushalmi (Sanhedrin 10:2) says there in fact were 12 Calves made because they desired many gods such as the god of Moab and the god of Edom in other words they desired the unique power of every nation. Why did they desire multiple gods? It seems that amongst the Shevatim themselves there were different views as to which god to chose and therefore each Shevat made their own god i.e, their own Calf. Consequently when Moshe came to give the commands regarding the Mishkan he first needed to unite them in one place for a common goal.

Sanhedrin (63a):Rabbi Shimon ben Yoḥai The verse teaches that the Jewish people desired many gods; they were not satisfied with the golden calf alone.