For dropbox, please see
What does it offer spideroak does not, why should another GTK app be added?
Explain about radiotray (also depends on GTK) too, what more does it stream, than say, clementine or vlc?
KaOS will stay limited in the size of the repositories, and will only add a limited number of the truly "must have, no other app provides" GTK applications.
If an application does not make it to the repos, it really s not hard to build it for yourself: