Well, they get the snuff out competition and get to hold on to IPs. The thing is though: People are saying that there are good indie games, but I won't ever hear shit about said games unless I specifically go looking for them, which will almost never happen nowadays.
Even when I allow ads, game ads are pretty rare. AAA games were almost impossible to miss because there's always enough buzz, positive or negative, for the big ones.
Well, as you can imagine, they don't have quite the same marketing budget. Many of them market themselves on social media.
Personally, I keep up with gaming news anyways, so that's how I'll usually find out about them.
If you don't do that, there's occasionally indie showcases where it's basically trailer after trailer for (already more established) indie titles.
Here's a recent one, which had some good stuff, albeit lots announcements for the future: https://iii-initiative.com
I'm sure, you can also find a million articles and videos for "best indies of 2023" or similar.