A very accessible video by 3ie starts with evidence from a recent study by the World Bank. It has found that a third of the research reports published by the World Bank on its website have never been downloaded by anyone and 87% never referred to in any subsequent research. This is extremely wasteful. Remember, our tax money pays for such research.
So the big problem is maybe not that too few research reports and evaluations are published - the big problem is that people don't use them, because they don't look for such evidence, or they find the reports too hard to understand. The latter can be dealt with by writing in a more accessible style. Finding time to think and explore may be more complicated.
In the meantime, you can use the evidence gap maps by 3ie to find out what research is available on specific areas - click here to get there (video 4, "How to use an evidence gap map"). The maps are based on systematic reviews by 3ie, which have also looked into the quality of the examined reports - a colour coding shows, how robust 3ie considers the findings. Where there is a body of existing research, donors can save a lot of time and money. Where there isn't, they can make a massive contribution by commissioning a systematic review in the field.
Of course, if those who commission research and evaluations published the reports more systematically, then the evidence gaps would be even smaller. So my plea to publish more evaluations still stands.