Hiya!
From other posts I think the response is usually if the program is not in the official repositories, it could be put in the Lite Software installer, i.e. not installed by default. Also, if a program is only in an external PPA repository, this applys too.
As for the program itself, I personnaly prefer XFCE from LL versions 4.x and up (3.8 minimum if obligated for 32bits). Previous versions give me all kinds of retro-headaches
.
Cheers!
By the way, there is a lot of development and error correction going on:
https://sourceforge.net/projects/classiclooks/files/
p.s. In my opinion this is one of the most successful themes of xfce in terms of harmonizing traditional old-school and new-school gtk3 applications and of course Gtk2 and Qt5.