Click bait is an outgrowth of payment in eyeballs.
As to virtue signaling, I bring that up because it can occur even if they are never mentioned on air. A company can say they are a corporate sponsor of X even if X only ever mentioned them on an obscure part of their website. In the world of virtue signaling simply accepting money creates vale. NPR is behaving rationally to accept as much money as possible and even to put effort into getting more because at effectively 90% the funding they would create less value, but clearly they could still create significant value with 90% of their current funds.
Anyways, if advertising went away, a massive amount of media you see today would also disappear. You would definitely notice that.
And that's before even getting to the even more massive impact it would make on the economy since every major company today relies on advertising for growth and sales. It's easy to look at few annoying banner ads and say that they suck, but this is a 12-figure global industry that plays a critical part in the economy. It's just not that simple.
Advertising is largely zero sum, it increases the cost of products while increasing individual product sales. People would buy almost exactly the same amount of food for example without any advertising so that's pure dead weight to society. Despite all those car ads people would still buy a car without them further without that massive cost those cars would be either cheaper or better, etc across a huge range of industries. Without ads people would still buy soap and other home goods, at worst they would pay less when doing so.
Virtue signaling is still advertising, paying money for exposure. Otherwise it's a corporate donation and that does not scale at all. You can look at the continuous travails of open-source projects that deliver billions in value but get no funding as a perfect example.
The point is that NPR comes nowhere near the massive amount of content that people consume but don't pay for. Please don't just assume the entire industry is incompetent, there are millions of people working in these media companies and they are constantly trying new options. So far, outside of subscriptions for certain high-end brands like the Financial Times, advertising is the only sustainable model found.