Test isn't about SOE or the players doing a favor for one side or the other. There is a mutual benefit to both.
For any business, having a group of consumers that you can trust to test you product, break it, and make suggestions is invaluable. Test is a different experience than a live server. People are less invested for the most part. People come and go. Hit it hard for a month, then disappear for a year. My interest in EQ wanes to the point that paying +$45 a month for multiple accounts is not realistic. Although I do enjoy playing when new content is released and report /bugs when I run into them. Big picture, I also have to believe that just simply playing there is useful to them as well. Whatever meta data they can collect on spell damage, class dps, failed scripting logs, etc has to be a major benefit to them to identify holes in their product.
The opportunity cost to SOE is pretty small in the scope of things. There are maybe a total of a few hundred accounts on Test that people would be willing to pay for. So really, they are missing out on maybe, maybe $3k-$5k a month revenue. If the free component goes away, the server becomes a ghost town used by internal developers only, which I'm sure already exists in some capacity. They certainly would be within their right to make Test player pay for their subscription, but it would be a "cut off your nose to spite your face" scenario.
