While there are RSS-compatible solutions for that (like AdSense in-feed ads), it is obvious that there is not enough financial incentive for content creators and platforms to continue supporting RSS. From consumer perspective, I’m writing this from Safari on iPad, and there is no way to see that RSS is present on the page, neither there is a way to subscribe to RSS without special plugins. Which tells me demand on consumer side also does not justify keeping these features up.
The only reason RSS is alive today is because it’s dirt cheap to implement, and is supported out-of-the-box by most web development frameworks.