Those studies cost money. For a comparative study you want probably a minimum of 12 users and you probably won't get them in a room for an hour for less than a $20 incentive. If you want them to be at all representative you're also looking at either buying access to an existing list of pre-screened users from a research company or spending a good 100 hours on the phone doing surveys. Think another few hundred minimum. A cheap comparative study, starting from scratch could maybe be done for $1000 but more likely is about $2500. You can do friends and family studies and pay nothing but you can never be sure about the data. In my experience developers also tend to want much larger sample sizes to "trust" results (think 1000-3000, political poll sample size). Not saying this is you but it shows how far the gap is between what some developers expect to see in user research and what user research does.
Aside from the costs of research, in the corporate world as a designer I don't have to do a study to justify every design decision to the developers. I understand why you want more than "because I told you so" but showing my stuff will work takes a lot more time and money than showing yours will so it's cheaper and faster if you can work on trust for some things. This is not to say you aren't justified in wanting more, especially from someone new and unproven but just to show that the open source community has at least the cost and trust issues if it wants to attract good designers.
There's also an incentive thing. If you want to make your name as a programmer open source experience can demonstrate skills, wide interests and passion to potential employers. If a young designer wants to design software and demonstrate skills, wide interests and passion they can do something in print, create a web site or small app by themselves. Something that will show off their design as they intended. "I got the XXXX team to agree to make slight changes to their configuration UI to make it easier to understand" may actually be a more useful and relevant skill to show in an interview but the poster, web site, or flash app you did will probably do more to get you hired.