Drugs aside I agree to a certain extent about genetics but from my experience Glutes on most people are the LAST place your body will tap bodyfat from ...and only once everywhere else is 100% lean The reality is one has to dig deeper to another level than you ever have before, and achieving that level is always a contest goal of mine. I believe once you are contest lean everywhere but the glutes, and in some people (myself included) hams are still not quite there (this is the stage most guys end up competing at and why it'd easy to think it's unachievable for them or others)..it takes another good 8-6 weeks of aggressive carb cycling,intense training and intelligent cardio to deplete the intra muscular fat in the glutes down enough to reveal those striations. It's tough and your mind & body will fight you - you'll deal with feeling of being near death, being really uncomfortable at times, insomnia and irritability - those low carb days can be quite spiritual actually
you have to have the mentality of one of those crazy free divers and apply it to dieting and cardio. this is not a recommended goal for a recreational dieter - purely for BB competition.
As an example (dark blue shorts) had been dieting for 18 weeks already - ripped but Glutes/hams still smooth. Then in the red trunks after another 10 weeks (28 weeks in total at this point) of carb cycle dieting (6 days low carb 100g/ 1 x 300g refeed - repeat ) and more cardio came down another 5 pounds (7 days out - Viola! Glutes finally starting to get striated) it just took a longer time in a deficit and being that lean already so my body had no choice and I actually have shit genetics for being lean!