I think this is a distinctly American perspective.
If one is born into a class/caste system, there are social agreements one inherits, rules one abides by since birth, that get one perks in that system. If someone in the next cubicle over (in a sense) isn't abiding by those social agreements and rules, it upends all my (and everyone's) diligent and life-long 'playing by the rules'. The 'upstart' gets 'punished' socially, maybe ostracized. Either they don't succeed in getting any perks ('only themselves to blame' for any hot water they find themselves in because they drew outside the lines) or they succeed wildly and make everyone else's obedient plodding 'nothing', 'fruitless', a mockery of their staying in the lines of the game as laid down since birth, and honoring those on the other side of the lines. It's no wonder resentment boils and bubbles in such social situations.
It also goes further: there are usually 'markers' for the classes. In some cases it is actual dialects that separate the 'high' (privileged/powerful) from the low (not privileged, not powerful), that bar transgression across the socially constructed 'classes'. In others it is genetic markers developed from generations of segregation (the skin color of the untouchable caste in India).
In America something unique developed in our national myth regarding transgression of the class boundaries, though in spades there are classes and markers between classes of people (skin color, ethnicity, religion, accent). The difference lies in the view of those that 'make it' to the top of the heap: admiration for work well done, etc. Instead of there being resentment, the reaction is: I can do that, too, or my children can do that, or my family can achieve that. In doing it, working for it, one is lauded, not resented. In fact, it has become a necessity to evidence such ambition or else be deemed 'lazy'.
So I think it's a cultural difference. The British view has got a lot of history behind it. It's when I see Americans opting in to the class snobbery of another culture that I find it perplexing.
If someone British would like to pop in, please do. This is all just the way I have figured it all out. Maybe I am wrong. JMO.