The reason they don’t is it reduces the chance of catering to publication bias–the tendency of editors to publish positive studies.
I know that blinding is essential to randomized controlled trials in medical research, but that reduces your chance of getting a result you’re looking for (note the use of the phrase, looking for, describes the problem of confirmation bias).
The really good studies are double blinded and cross over, when the inquiry allows–blind subjects and researchers, study the control and experimental groups that are properly randomized and matched, then cross over the subjects and redo. Reduces chances for outcome or confirmation bias by a bunch, since hypothesis driven biases always impact the behavior and judgments of the researchers.
So here’s basic stuff, ignored particularly in the soft social sciences research–ecological research, political hot button research.
Reason is blinding might result in too many studies that are not going to get published, and researchers like to produce research that pleases their sponsor.