You might want to ask around about why they don't use it. And you might need to probe beyond the surface, non-thinking, "because I didn't think of it" answer.
For example - I've been in situations where I used email instead of an internal wiki because:
The wiki was really hard to use, and too time consuming to maintain - especially in terms of cross linking and organizing information.
- Possible fix - depends on how in control the team is of the wiki software. For example, in a massive corporate environment, it's not particularly easy to customize something like Sharepoint... but in a small team it may be able to tweak the GUI so that it fits the team's style better. Also, a big part of this is cross linking - the easier it is to search and cross link topics, the more enticing, since it trumps the painful searching of email.
I honestly believed the information had a short lifespan
- IMO this is a reason to not use the Wiki. If it's a short term thing, it doesn't need to be archived the way most wiki material is archived. If there's a status that is changing, but always in existence (for example a server tha is either up or down) then may be it can have a dynamic web page attached to the wiki, but that's not exactly wiki content, either.
I honestly felt that everyone needed to see it, and I was worried that "hiding" it in the wiki would mean that it was only available if actively researched, rather than passively received.
- This is sometimes mitigated by poking people to paste their email into the wiki and then send out an email with a link. In many cases in my office this could become a self reinforcing thing, since most people preferred short sweet emails with a link for more detailed info.
- Another trick was to enforce this as a culture thing - we enough team changeover that people were inspired to wiki-ify something when they knew that the next new guy would need it, too, and putting it in the wiki now meant not having to dig it up later.
I had no good guidelines for what should go in the wiki
- As a team lead, I led by example. Our best wiki information started with content that I laid out, then people told me that it needed an update, and I asked themto update it themselves on the wiki. When an area had a critical mass, then it got more play for further growth and enhancement. It was like the wiki needed to be "seeded".
I wasn't using the wiki to get my information, so it didn't occur to me to fix the information that was there.
- Can be fixed by a combination of good finding-mechanisms - searchability, cross linking, content related suggestions, and other navigation tricks. And by the "seeding" of the wiki with useful content that exists no where else. If I had it to do over again, I'd move all our old pre-wiki "How To" documents to the wiki, so that there was no doubt where to look for useful information.
I know that in my teams we've had trouble switching from other communal forms of data sharing to a wiki-based format for reasons like this. In these cases, a badge system wouldn't have helped... it really took the elimination of mental barriers to entry.
I'd posit that while I like getting the "cookies" on the StackExchange sites, another reason I keep coming back is their immense searchability and the ability to get good content. If either of those qualities were missing, the badges wouldn't keep me around long.