I wrote gnome-power-manager a long time ago, and then a old dead
branch was forked into mate-power-manager -- my code was incorporated
into gnome-settings-daemon and improved upon and further pushed down
into the stack. I don't think there is anyone who cares about the
long-obsolete mate power management stuff. Basically, MATE is a mostly
a fork of old GNOME components, and the developers who wrote the 99%
code shipping with MATE are either not working on Linux any more or
are working on GNOME. I think over time MATE is going to become harder
and harder to maintain. Sorry to be blunt.
It's under active development, doesn't mean that the original developers
who's code was forked need to be on board. MATE is now completely GTK2-free
since 1.18, and looking at the roadmap, this seems to provide the option
of reintegrating some current Gnome3 components.
Power management is a weak point right now.