Class matters most to those on the precipice of their class distinction. If you're old-money, and your entire social circle is old-money, then you don't view the things you do as being "high class", they're just normal things you do. So it goes with the middle and low classes.

You see the most obsession with class concerns in areas where you have people who are class mobile: There's a lot of nouveau riche and upper-middle class people in tech, because tech has been a massive boom industry. Likewise you see a fair amount of class concern among people falling down the social ladder, such as the generations that grew up within environment of an old-money fortune, but for whatever reason that money was lost.