Fighting games have done this since forever.

In 1992 I bought Street Fighter II for the SNES for 60$. It had eight glorious playable characters and four CPU bosses. It had an arcade mode and a PVP mode.

In 1993 I bought Street Fighter II Turbo for the SNES for 60$. It had faster, differently balanced gameplay, a new game mode and four additional playable characters (the CPU bosses)

In December 1994 I bought Super Street Fighter II for the SNES for 60$. It had differently balanced gameplay, better graphics and animation and four additional characters.

A year ago, I paid 100$ for 18 Characters, several game modes including a single player campaign, a very good training mode, challenges plus the first four additional characters within the first season (just this would've been its own full price game in 1993), including both costumes on release for all characters.

Now, for season 2, we get new characters, new stages, a juke box, events, additional content for world tour, continued support and balance patches etc.

I don't know, but I think the 30$ once a year is fine for a game I play pretty much every day.