I'm not sure how active desktop development needs to be for a single *nix desktop environment.
Back in the day, it was the difference between useful and soon to be useless, but these days not very.
It's also not really that vital that all the applications I use are the ones provided by my desktop environment. So Konqueror hasn't really kept up? Big deal, I mostly use a mix of Firefox and Chromium anyway. KMail old and ugly? Doesn't matter, I never use an email client these days. And if I did, it would likely be Thunderbird anyway.
So all I truly need from a desktop environment is that it looks and behaves the way I like. KDE is, and has been for a long time, the best at that for me. Will I some day want some features from my desktop environment that KDE doesn't provide? Possibly. But until that day comes, I don't much care how actively KDE is developed, as long as it continues to work.