Why does everyone want to "improve on BitTorrent" by adding content searching?

Every single P2P client except BitTorrent has searching. BitTorrent beats them all out in popularity, often by orders of magnitude. These two facts are not completely unrelated.

BitTorrent is so popular because it is minimalistic, and uses the web to catalogue the content. People already know how to use the web. People don't want classic P2P app with a confusing interface and strange behaviours and rules, they want to click on a link and get their file. And that's what BitTorrent does, and that's why it beat out all the clients that already exist and do exactly what BitTorrent does except with content searching.