Their own lives were comfortable and easy in the middle class. Risking it all for revolution to help other people is not in their class interests.
The middle manager is still being exploited by the CEO, sure, but lets not pretend like the middle manager is a potential revolutionary. How much better could their life actually get? They have a home, vacation, healthcare, education, leisure time, and all the toys they can buy.
But! Like I said, as the American empire declines that changes drastically. Without cheap 3rd world labor to superexploit and with the decline of their own middle incomes, they’ll quickly find their comfortable and easy lives disappearing. Suddenly the middle manager isn’t so different from the rest of us down in the dirt, and the CEO will still be raking in millions and billions off of their labor.
Once bourgeoisification is reversed, the middle class ceases to exist.