In fact, they were proper names of different deities. Unlike El, Yahweh was envisioned as a storm god in the early literature, one among many Canaanite gods and goddesses including El, Asherah and Baal. Eventually, Yahweh and El were conflated, and became chief among gods. But Yahweh/El was not the only god worshiped, not until Elijah rose to prominence. For a very long time, Yahweh/El was not the only God, just the only one that had any sympathy for the Israelites.