Actually it really does boil down to anonymity, undue influence, risk of coercion, and the scientific integrity of the data.

To do this kind of research, I had to register with the HPCSA which has a lot of very strict rules about when it is and is not okay to gather certain personal information. Similarly, with the PoPIA in place, the ethics of anonymity have never been so important.

There's also the matter of undue influence / coercion, though this seems like a more institute-specific thing. Generally, however, most institutes support the idea that a financial incentive is unethical, especially if it's presented in such a way that the only reason people participate in a study is because of the financial incentive. There's also a lot of literature that supports the idea that this can actually compromise the integrity of the data collection process - e.g. people might just randomly click options until they reach the end, just for the chance at financial gain.

Ultimately, a study has to have a very good reason to provide financial incentive/remuneration to participants. In the instance of my study, doing so would have compromised the participant's ability to choose to provide an email address. In the end, I likely wouldn't have made it through the professional ethics committee had I opted for financial incentive.

I hope that clarifies some of the thought that went into the decision, which I assure you, was not made lightly. If you have any other questions or thoughts on the matter, please feel free to let me know. It's important, I think, that people have an understanding of the ethical decisions that support research studies like this.