There are some benefits (incentives) to running your own DNS server with the ability to perform recursive queries, but best practices dictate that these servers should only accept queries from "trusted clients". So, it's not so much that there are incentives to run an open recursor as it is there are very few negative incentives to running an open DNS recursor. I keep highlighting the word "open", because the open state of a DNS server is often not an intentional decision.

I'd speculate the most common reason for using DNS recursion is to allow a non-authoritative name server to return results for any query. This non-authoritative name server usually sits on a network that serves clients with low latency and high bandwidth, like a LAN. The network is typically private, but private is not always the same as secure/closed. Some benefits of running your own DNS are:

* The ability to cache DNS lookup results (speed increase)

* Placing the name server closer to clients (speed increase)

* The ability to blacklist certain zones (security)

And many more, most of which relate to control, speed, and security.

The thing is, none of these advantages are related to running an "open" DNS with recursive queries enabled. I think the core problem is twofold:

1) Many amateur sysadmins don't recognize that running a name server with recursive queries enabled is a security issue.

2) Enabling recursion doesn't automatically require any configuration to secure the client-trust relationship.

Unfortunately, I'm not really smart enough to propose any changes that would help the situation, but I think this represents a high-level overview of the most common problem scenario.

EDIT: It's also worth noting that some DNS servers enable recursive queries by default. Anyone running their own DNS for their zone, but who don't have knowledge of the issues related to recursive DNS will likely be running an open DNS recursor as well. These are commonly servers at web hosts, which have much faster internet connections as well. So it's a matter of getting everyone on board for changing defaults.