> Maybe I have an incorrect view of the costs/revenue.

I run Weird Gloop (the group hosting the Minecraft/RuneScape wikis) and your view is generally correct. The content is extremely cacheable and the infrastructure costs have extremely strong economies-of-scale. The labor costs are a bit less obvious, but past a certain baseline (of, say, having enough people for a reasonable oncall rotation), the marginal labor cost of hosting additional wikis is quite low.