> Why isn't that happening?

Because most podcasters make no money and don't have the skills to write an app or service to do it for them.

Larger companies like NPR and BBC already do it.

OP's concern isn't about individual producers. It's about media and tech companies like Spotify and Stitcher gobbling up the market.

Because right now they're counting on the fact that some percentage of the listeners won't skip the ad, especially if it's the first time they're hearing it.

Make the ad-skipping automatic, then it's guaranteed that no one is listening to ads. (no ads == no revenue). This will completely ruin the system as it exists today.

Because nobody can prove people are skipping the ads. Maybe they are, maybe they aren't, if you make an app that's sole purpose is that and it becomes massively popular then you know a huge chunk of the audience is skipping said ads...

No, what's going to happen is that this will kill independent podcasting and make it unsustainable to run a podcast without agreements with Spotify or Apple or someone.