People have been talking about new ideas as the basis for keeping people on Blockland, but it really isn't. The Island TDM Dogfight has been used countless times, and yet Heed still gets roughly 20 people on average on his server at one time. I don't think it's originality, thus imagination, that's the issue, I think it's a general degradation of the Blockland society that was inevitable.
Think about it like this. At the very beginning of the game, when it all was brand new, there were a few people who played the rather archaic game that was just building. These people were ages 10-16. The older people grew up and stopped playing at that point, but the younger still played, and learned. At this point, Blockland got better and more comprehensive. People became hooked on it, and more people, of around the same age as those same people, began playing. The older people then began making addons and building great builds, doing coding and stuff, and so made all of our addons and good servers for us. This is when a group of young players began playing, and the fad slowly grew in their age group. This continued to spread, and we got more noobies. Our old, addon making, good server hosting people were still pumping out addons and hosting good servers, so no one needed to step up and be addon makers. Then, these old people began leaving, because they grew up. So, we were left with a few good servers and only a couple addon makers. The noobies, who are now old, never got into making addons or good servers, because they were used to playing only. The newest newbie gen came in and are too young to do any of that well. With V21's premier, the old newbies began leaving because they were used to maps and interiors. The few old newbies left standing are now trying to make Blockland better with more addons and good servers. This cycle will continue on forever.