I feel the same. A lot of big projects fell by way side over time for various reasons. Goes with the nature of experiments, sometimes you win, sometimes you lose.
k3b - died with the cd-rom
calligra office - creation of LibreOffice stole the thunder
konqueror - maintaining a secure browser that isn't a fork of chrome is a tall ask these days
amarok / kmail - rewrite lost features, introduced bugs, and many existing alternatives filled the gap
That said there are still a lot of good ones still there that continue to improve every day. Kate, dolphin, KDE connect, etc.
k3b - died with the cd-rom
calligra office - creation of LibreOffice stole the thunder
konqueror - maintaining a secure browser that isn't a fork of chrome is a tall ask these days
amarok / kmail - rewrite lost features, introduced bugs, and many existing alternatives filled the gap
That said there are still a lot of good ones still there that continue to improve every day. Kate, dolphin, KDE connect, etc.