Simple: No upside, plenty of downside.
Most the most part, studies are initiated to confirm the efficacy and safety of components which are to be turned into products. This world is insanely corrupt. I grew up in the 80s and 90s, and back then studies showed that butter was proven to be unhealthy due to saturated fat content, and margarine with trans fat was touted as the healthy alternative. Could it be that using a byproduct of growing canola and soybeans was cheaper and easier than raising diary cows? The FDA has since added strict limitations on the amount of trans-fat that margarine producers can include in their product, but this happened a quarter century later.
While I doubt this is a huge factor, consider the massive list of warnings that come with a pharmaceutical advertisement: Feelgoodpills may cause increased heart pressure, dizziness, blackouts, bowel disruption, vomiting, nausea, headaches, tiredness, if you’re on other medications please consults your physician. If you’re pregnant, over the age of 50, or lived in Flint Michigan or five years or more, please seek alternative options. Do you know how this list is created? A study is done with n people as the control group, and n people as the placebo group, over however long of a period of time is required to validate the claim. During that time, any medical condition that befalls any of the members of the control group must be included on the side effects list, even if it is plain to see that the medication did not cause it. So during the trial, if one member of the control group gets food poisoning, and could even identify the shell of the oyster that caused it, every symptom that comes with the food poisoning is now legally compelled to appear on the warning label because he was part of the control group during the study. Most medication isn’t something that people want to take, it’s generally a necessity, so the side effect warnings become secondary. If a doctor tells you you need X medication for Y effect, you’re generally going to take it. Nobody needs PE like they need might need penicillin, anti-psychotics, or even Viagra. Seems to me like it would be a hard sell when included with the random trial-induced side effects you’d also have to include all the effects incurred by the folks who did it wrong: loss of erection quality being at the top of the list.
If there’s no product to sell, there’s no money to be made, and no reason to make a study. No upside.
As for the downside, when performed incorrectly, PE can be very damaging. Sure independent individuals can make expensive training videos of jelqing and stretching exercises, but can you honestly imagine an established corporation risking it’s coffers against the litigious nature of Americans who have a tendency to act first, think second and sue third?
I don’t see it happening any time soon, and especially not as a product of the mainstream consumer machine.