[kbolino]

What matters in the long run for making a good wiki are the people and policies.

Young and niche wikis are happy to take any contributions they can get. The quality and timeliness of any given bit of text soon ends up wildly different from page to page or even section to section. Some people may decide to take their time not just contributing new content but also editing existing content. However, it becomes difficult to balance creation vs. curation. Too much creation, and the editors get overwhelmed, and then the users can never be sure what to trust, and so the wiki becomes irrelevant. Too much curation, and the information becomes uniformly stale and lowest-common-denominator, so the users start going elsewhere, and so the wiki becomes irrelevant.

Different wikis means each one can have its own people and policies. If the people who made one wiki great leave, there are still other wikis out there. If the policies choke the life out of one wiki, there are still other wikis out there. Some wiki can be full of deletionists while another wiki is full of inclusionists. Some wiki can be full of mergers while another wiki is full of splitters.

Forcing everybody onto one wiki forces them all to work together, but this is an entirely volunteer effort, and so many will just leave. Even if they were paid, some individuals would dominate while others would get crowded out. One can point to Wikipedia as a glaring exception, standing as basically the only wiki of note of its kind, but I think it's the exception that proves the rule.

[kayodelycaon]

Wikipedia is definitely the exception. It works because almost everyone on the Internet uses it.

[account42]

And it's not without problems, not the least of with is that being the default Wiki attracts the kind of people would would love to control the definite source of information.