I'll bite, beandip.
Inequality in our real world is horrific; inequality in Sindome's world is exponentially higher. The corporations won. There are barely any laws or regulations to limit their pursuit of profit. They are reaping extreme profits, with the junior-class corpies receiving barely any, while the executive class controls obscene amounts of wealth and power. It's difficult to even imagine what C-suite executives at Sindome's megacorps get up to in their free time.
All this profit comes through unrestrained exploitation. The megacorps are focused on influencing and squeezing the masses to drain them of every drop of productivity and consumption. That millions of people live in hyperviolent squalor isn't an accident. It's what the elite want. It's a captive market who has to live hand to mouth, who are desperate for any relief from their terrible existence and will pay for brief respite real or imagined, who have no options to seek better than the low-paying, menial jobs they have, if they're even able to hold down a job.
Most Mixers (in the sense of including NPCs and virtual NPCs, the full tens of millions of them) cannot push to go topside. They don't have an education. They've suffered from malnutrition their entire lives. Their brains are stews of stress hormones and an always-on fight-or-flight reflex. In our world, people born into the lower class rarely leave it, and it isn't lack of will that keeps them there. It's lack of opportunity. In Sindome, just like the inequality, this is exponentially worse.
PCs have the capacity to be special. But they're still drawn from the world's population, the vast majority of which is downtrodden by the system. They've seen the effects of it for their entire lives. And at least when a PC first immigrates, their stats are bad. They're supposed to be a weak, unobservant, unhealthy, ugly, stupid, slow, unlucky castoff from society. Most of these people would have no shot at a corporate job. Instead, they see the inequality in Withmore shoved into their faces from the start.
Why should mixers, most of whom have no opportunity to ascend, look down on those who do, and hate them for selling out?
Because the world of Sindome is zero sum. The corporations are making their profits by using up and exploiting people like mixers. And they're maximizing that profit, unrestricted, at every turn. There are no laws about factory conditions; there are no laws about what can or can't be put in mass-produced food.
From the perspective of a mixer, this is all at your expense.
If I, in my real life, met a person who told me they work at an oil company, choosing drill sites? I'd probably hate them. They and their company are profiting off of the climate disaster that is going to make my life worse.
If I met a political lobbyist who worked against free elections? They're paying their bills with money earned by making my life worse.
At least from my perspective, Sindome's corporations are (among) the bad guys. Unfettered capitalism is not a good thing. It consumes and destroys.
Now, this is a Cyberpunk game. Cyberpunk stories aren't black and white. They're grey. And cyberpunk stories aren't tales about heroines and heroes who triumph over the system and produce revolutionary change. They're stories about people who fight for small victories inside a system that, if they are opposed to system, either corrupts them or kills them in the end.
It is very common in cyberpunk stories for characters to make moral choices where they choose either their personal values or the profit, power and safety of submitting to the system (an example off the top of my head: Takeshi Kovacs going against for emotional reasons despite great danger and lots of reasons not to). That conflict with the system has to be present; every character is somewhere on the spectrum of having conflict with the system (even Randian corporate supercapitalists who'd sell their own mother for a good annual review will eventually put their own interests ahead of their corporation's and make a choice at odds with what the system wants them to do). Some characters will be close to the extremes of cooperating or not cooperating. There are good cyberpunk stories to be told at both ends.
The argument can be made that currently, players do not allow enough room for Mix stories where characters are not opposed to the system, where they accept it as the order of things and want to rise in it, and where they work inside the system. That can be a legitimate discussion.
But it's perfectly reasonable for a person living in the world of Sindome to hate the system they find themselves forced into, under the weight of, and to hate the people who admit to, even aspire to, perpetuating it. That's both logical and cyberpunk. There being "too much" of that kind of RP is a different discussion than it being somehow unthematic.