You almost never see supplements with a 1:1 ratio or a higher DHA ratio, it’s always a higher EPA. I have read that there are benefits and negatives for both types in different ratios so why do almost all Omega 3 supplements always have a higher EPA ratio?
My guess is that the source material has more EPA. Most species that produce omega-3 (without having to eat them) do so by elongating ALA to EPA, then elongating EPA to make DHA. Also, DHA can undergo retro conversion back to EPA, if the cell desires more EPA.
You ask a very interesting question. I don’t know exactly why Omega - 3 supplements contain more EPA than DHA, but it might explain why studies have shown no cardiovascular benefits from taking Omega - 3 supplements, as opposed to those studies that show that fish consumption reduces the risk of CVDs. The effects of DHA and EDA on lipid metabolism and their antiinflammation effect are similar, but not identical. A comparison of the effects of EDA and DHA can be found in these articles https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146314/ https://academic.oup.com/ajcn/article/104/2/280/4668547