I see two reasons for low participation of the group.
1. The RE Market has cooled a lot. There are few transactions as
compared to the last year or two, hence the need to seek and share
info is reduced.
2. Even though MSN groups had its own limitations, by virtue of being
in use for a long time, people had got used to the site and were able
to navigate easily. Some how the google groups is somewhat cumbersome
to use.