Diane -
I know what you mean.
I also believe that the group declined for other reasons as well. This has also been true for various e-mail forums of various topics. UC Davis has confirmed for me that overall listserv traffic has been decreasing over the years.
Personally, it does not seem worth trying to keep Medit-Plants alive. It had a good run - as shown in the archives saved on Hort.net (if anyone is unaware of this archive, check it out -
https://www.hort.net/lists/medit-plants/).
Perhaps hardest for me, as creator of the group, but there you are.