I agree that two-line entries are harder to add to. So, it's less likely that people are going to continue them, though it's not entirely impossible.
Perhaps, it's because a two-liner only presents an idea without any narrative momentum. Whoever adds to it has to expand on the idea AND build up that momentum. It's a lot to ask of someone, especially for an idea that wasn't even theirs to begin with.
In the end, you'll have to be patient.
