The most important characteristic of any internal documentation is trust. People need to trust it. If they trust it, they'll both read it and contribute to it. If they don't trust it they'll ignore it and leave it to rot.
Gaining that trust is really hard. The documentation needs to be safe to read, in that it won't mislead you and feed you stale information - the moment that happens, people lose trust in it.
Because the standard of internal docs at most companies is so low, employees will default to not trusting it. They have to be won over! That takes a lot of dedicated work, both in getting the documentation to a useful state and promoting it so people give it a chance.
Eventually the quality drops to such a level that some poor bastard spends their time bringing it all back up to standard - and the cycle repeats.