Are supposed to, but doing that would require so much more work than is usually being put into it now. Especially in the first rounds, it would be impossible to review all candidates/proposals thoroughly without having staff dedicated to just that. (IMO institutions should have such highly-skilled staff.)

It may be true that the SNR in research output from developing countries is lower, but there is still lots of good science. But essentially no publishers with good reputation. So even with the same SNR, the increased pool of countries producing science would add to the publication pressure.