Single-purchase retail like Starcraft 1 & 2 simply doesn't make sense as an exclusive revenue source for small studios anymore, you're not likely to sell enough copies. The revenue isn't there. You've got to sell cosmetics, battle passes, or (barf) put in a gacha system. I'm not happy about it as a game dev but it's the reality. Even big games like Destiny 2 rely heavily on those microtransactions to rake in the cash. :(

This is especially bad for multiplayer where you need high player counts so people can get into matches quick. Indie multiplayer games HAVE to be free or very inexpensive.