I guess this is a problem that's mostly network-wide.
One things that SE does differently than a lot of other forums is that you, as normal, avid user, can actually gain rights to become a little helper of the moderators. You can actively edit post, vote to delete them, organize tags and so on.
Many users may not be used to this as the gamification system is progressive and unlocks "features" by gaining reputation. There's no one universal who approves your actions and you are basically left alone to figure out how things are working. There's no advisor who says what is best practice or how things should be preferably handled. By not having a person who approves your actions, users may feel uneasy about particular tasks. They might feel that uneasy that they just leave out to fulfill their "duty" to help out the community (a major point of a progressive reputation system).
How can you get more people to edit posts?
You start off by telling the users to edit their own posts. In a large community, almost always there's someone guarding the place by editing single posts to increase the overall quality. Don't do that. Show users that they can correct their own mistakes by clicking the edit button. Tell them what they should do:
- Can you provide additional information, please?
- Can you clarify your question, please?
- Can you edit your title to match your question, please?
All these requests help to lower the fear of doing something wrong. If you encourage users actively to correct their own mistakes by showing them the best practice, they will grow confident and become self-reliant. And self-reliance is what you want to achieve in this kind of reputation system. Show them how to do it and they will execute it that way.
You can discuss the matter on the meta site corresponding to your main site. It's an issue which is a bother. If it bothers you, you can discuss it. Say that you think that more people should edit so they actual workload among the regular editors becomes less and the review queue is cleared more quickly. Most users won't do anything if you don't ask them to do something. They follow rules because they read them. They follow guidelines because you asked them to do so. They don't edit because you haven't asked them.
The key problem of a self-moderating community is that you usually don't have a sandbox to test out your corrections and rights. Everything you apply, if you have sufficient reputation, is put in place immediately. Just imagine someone just reached the threshold to cast a close vote, would you like to mess it up immediately? I don't think so. There's a delay between actually gaining the technical power and the ability to apply.
Imagine that you are hired, you're new to the company and you don't know your colleagues. Even though you're in the same position, you don't know how to use your newly gained rights. You need to get the hang of it. I haven't started immediately reviewing as I gained the right, I needed 500 more reputation to feel confident enough. One thing you should consider here that users who participate in others communities and already have gone through such a learning process are going to edit way more quickly. They just have to get used to the sites practices and the people, but not to the technical power.
Eventually, there's the point laziness. Even though, you gain technical power, there are others users who gain power, too, so there's no need that I must help, right? This can be the thinking of some users, there are lots of others users who have the same or even a higher reputation so they should be able to take care of the formalities. This is a common misjudgement, even in other communities. You have to get it straight. Everybody is absolutely welcomed to help out so the workload is getting smaller. You, as user, are encouraged to help out to help other users by getting their posts reviewed and answered faster.
The summary of this is:
- Encourage your users to edit their own posts to become confident and get used to your way of handling things.
- Discuss the matter on your meta site and ask for the opinions of other high reputation users and reviewers.
- Encourage active helping. Everyone who helps, helps another new user. And never forget: We were new to this site somewhen too!
- Take the little delay between gaining technical power and gaining the ability to apply it into account. People need to get used to the technical power be able to do stuff (if they haven't been a moderator in the past or are high reputation user on another SE site).
- Build up self-reliance. If users can solve problems themselves, they most likely have the confidence to tell other people how to solve problems.
- SE is based on a progressive reputation system. In order to make the best use of it, you should give advise to those seeking it. Explain to them how things work and redirect them to detailed help pages so they can get the hang of it.
If you are open-minded and helpful, other users may feel encouraged enough to help out by reviewing. You have to minimize the factor of fear. The fear of doing something wrong.