You're right on what they're doing, but not the why:

1. They're getting the short end of the deal with music licensing (as are artists, btw)

2. They can't pay the artists more: the vast majority of the money goes to labels

3. The only way Spotify can grow profits if it moves to content that's not under the iron grip of the labels: podcasts, audiobooks, etc.

See https://news.ycombinator.com/item?id=47783435

You're forgetting:

4. Once Spotify wrests power from the labels, they start the enshitification process themselves.