First NPR didn't come out with phc or car talk in the first place. They were both produced by affiliated local public radio stations and then syndicated (phc is an american public media syndicated show for instance).
Second affiliated stations are still producing great national programs. Stalwarts like "this american life" and "on the media" or newer shows like "the moth radio hour" seem to directly contradict your statement.
You mean charming radio unfriendly experiments that slowly build up deeply devoted followings over time?
Might see something out of left field from a member station, it's hard to say. Podcasts are doing alright though, probably providing more variety than NPR could ever support.
There's something about the usability or delivery of a radio station though. Low budget college stations and shock jock conglomerates are equally accessible to any user. For a niche podcast to take off, it needs exposure. People need to learn what a podcast is and how to download it.
For NPR shows, well, they were already beamed into everyone's homes. If users just dialed through the static, something they already knew how to do, they'd hear it.
Second affiliated stations are still producing great national programs. Stalwarts like "this american life" and "on the media" or newer shows like "the moth radio hour" seem to directly contradict your statement.