Long Post, so TL;DR at the bottom:
It goes back to boomer culture (as everything does). They were handed the greatest economy that the world has ever seen. This means they never had to worry about social responsibility. The main concerns and moral imperatives that the boomer generation created was purely about personal responsibility. For the largest demographic it boiled down to “Everyone's needs are met and everyone has the opportunity to succeed, so I just need to focus on myself and my own needs.” another more analogous way to put it is: “I can assume my neighbor's bowl is full and just focus on if mine is full” This was because, for the most part, that's exactly how it was. This created a culture of self-reliance, if you couldn't succeed, it was your personal failing not the fault of a broken system. This bleeds into and colours *EVERYTHING* that came from that generation. Including the morals they tried to instill in their children, some of whom do follow that now toxic belief and have internalised it to dangerous degrees.
Now, to the crux of this post: Discussing salaries goes directly into all of that, it's looking in your neighbor's bowl, it violates the boomer ideology of “stay in your lane, and focus on yourself.” This is also why they feel that politics and religion are things you don't discuss either even though it has led to a generational problem with ignorance in both at this point.
This is why the Millennial and Zoomer generation are different. As a society everything has failed to the point where if your bowl is full, it becomes your responsibility to help someone who's bowl is empty because unlike the boomer generation, there is a realisation that it's *NOT* their fault. There has been a fundamental shift from valuing personal responsibility to valuing social responsibility. This colours everything in the behaviours of all of these generations. Unions? Stay in your lane vs. we are all in this together. I am sure you can think of many many other examples of this.
This isn't corporations and capitalism that started this by design, but rather they have weaponised it and taken advantage of it and wield it like a cudgel.
This is also perpetuated on the human need to believe that nothing changes, that if you haven't experienced it personally, then everything is the way you remember it as you have no personal experience to contradict it, what changes have occurred are alien to you. This is also why these people are hard to get through to because they can't conceptualise what they have never experienced, it's not a failing, it's just psychology, though that doesn't excuse it either. To combat it requires different tactics, I don't know what those tactics are, but I am trying to find them.
My worry is, if this generation creates another generation of equality and equity that there will be another generation that grows up in that and then summarily pisses it away and becomes as self-centered as boomers after all the trouble it will take to get there.
TL;DR: Boomers grew up in a generation that only needed to focus on their own needs because of the systems of equity their generation had and so it created a culture of “stay in your lane and only worry about yourself”