I took a brief look at the Dream Aquarium forum, and easily see what you mean. I hope you don't mind a question.
As someone who has been there a while, to what do you attribute that difference?
There has been so much activity since you asked the question, I am unsure that you will be interested in my answer. Anyway.....
I must acknowledge that both MA and DA are the creations of two extraordinary programmer / graphic artists, and I am not offering any opinion on the merits of one over the other. Similarly the forums that have built up around the products are different and will appeal more to some people than to others.
Here are the differences as I see them:
a) The creator of DA (Alan Kapler aka spidermonkey2001) is a one-man band. He is the sole programmer of his product and is the administrator of his web site and forum. There is no equivalent to feldon34, Edgar and Prolific Publishing.
b) The MA forum which started in Dec 2000 (?) is more mature than the DA forum which seems to have started in Dec 2005. Surprisingly, the difference in the number of registered members is only about 330 in favour of MA. The MA forum has developed into a 'meeting place' forum whereas the DA forum is still essentially one that is built around the DA product.
c) Unlike Jim who has an almost constant presence in the MA forum, Alan has a more disciplined approach to his forum (possibly because he has to earn money in a 'real' job elsewhere). He tends to visit suddenly, announce a new simulation feature (eg to add a Marble Angelfish with virtually an unlimited array of different patterns), handle and respond to the flurry of beta testing and then disappear when the product appears stable. He will occasionally visit (as he did early this week) to answer requests and attend to order / serial number problems. It might be months before he re-appears.
d) Like MA, the DA forum has a very small band of 'helpers', as distinct from beta testers. One, in particular (A.P. Wesseling) typifies the difference in attitude within the forums. He has produced a script that enables users to easily choose settings that control the fish size, school size plus much more. There has been minimal impact on Alan's time, and the forum members have been appreciative rather than hostile.
I continue to visit both forums daily. When and if something happens over at DA, SOMETHING happens! There is always activity here at MA, but I am not sure that it is any more productive.