First, you’re right that several EA psychology researchers are studying how people donate to charity. But most of them (including myself) are also studying other EA-related topics, such as the psychology of xrisk and longtermism, moral attitudes towards animals, etc. My hunch is that only a minority of currently ongoing EA psychological research projects have charitable giving as their primary topic of interest.
Second, as David pointed out, donation choices are a useful behavioral outcome measure when studying the public’s beliefs, attitudes and preferences about EA related issues more generally. In many cases, the goal of the research is not necessarily to understand how people donate to charity specifically but to understand the fundamental psychological drivers of and obstacles to EA-aligned attitudes and behavior more generally (example). Studying these in the context of charitable giving is an obvious and often straightforward first step — in the hope that these insights can be generalized.
For example, the fact that people are willing to split their donation, as described in the post, tells us something more fundamental about people’s preferences structure (the fact that most people value effectiveness but only as a secondary preference), the potential market size of EA in the general public, and possible routes for reaching a wider adoption of EA ideas. Another example is the study of individual differences: who are the people who immediately find EA ideas appealing, where can we find them and how should we target them? It’s natural to test this, in part, by observing people’s donation choices.
My view on prioritization is that psychological research can be useful when it yields such fundamental insights. But there can also be really useful applied research, such as marketing or psychometric research that can be practically useful for recruitment.
Can you elaborate a bit more on what you consider the distinction between fundamental and applied research is, here? (To be clear I’m aware of the usual distinction, I’m just confused about how it’s applicable here).