Why do PhD students do research for other people’s research ideas? I’m a research assistant with an idea for a new study.  I’ve started my literature review, however a couple of people have said to me there are plenty of PhD students who would be keen to help with the research.  Why would a PhD student want to do research on a topic that’s not potentially of any interest to them?
If they want to help, it implies that they are interested. Multiple people can work on research projects and get a benefit from them. 

I've helped on numerous projects and ended up getting a name on the resulting research paper. I wasn't able to use that research in my PhD thesis, but any job applications look a lot stronger as I have experience in a good variety of projects.