If we go through the meta-questions of individual sites, we can also find a lot of differences based on what is on-topic on a particular site.
No one can deny that they are highly related or overlapped to each other. So, it is clear that the users, whether beginners, intermediates, or experts, can contribute to the three sites based on the questions asked. But it can be noticed that the users contributing to all three or at least two sites are rare.
The reasons I'm thinking are that the users either are interested in contributing to a single site or may be unaware of the questions on other sites.
The latter reason can be at least slightly fixed by streaming the hot questions on the other two sites somewhere on the main page of the third site.
It will provide users an advantage to read at least two to five hot questions on the other two sites so that they can diversify the contribution.
Do the members of the Cross Validated stack exchange welcome this feature?
Since I am sure that Artificial Intelligence community is ready to ask this feature, I asked the same question only on Data Sciences meta .