Roughly, the National Science Foundation - NSF and National Institute of Health - NIH get some of the ‘top people’ in a field together in a room and ask them “what programs should we pursue?” This process depends first on being able to identify the top people in a field and convince them to stay in a shitty hotel in Washington. So the agenda is being set by ‘the top people in a field who are willing to come to Washington and stay in a shitty hotel.’ Additionally, who entails the ‘top people’ is up to the program officers and since Professors have long term relationships with their NSF program officers chances are that the professors who have put the work into those relationships are going to be the most salient.
All the incentives are set up so people probably push for their lines of research. Even if they are being completely intellectually honest, researchers probably think that their area of research is the most important thing to fund. If they are slightly less intellectually honest, they realize that they’re more likely to be funded if their priorities line up with the NSF’s.
The process is inherently conservative All the incentives in research drive towards conservatism because if you’re consulting the top people in a field on what to fund, the chances they’ll suggest the weird new thing are low. This is another reason why Younger professors have to spend more time getting money.