Business Insider did an article in the past month on the "unnameable malaise of the middle class".
When you look at the 4 biggest expenditures of healthcare (including insurance), college tuition, rent/mortgage and food, costs were going up 3% a year for the past 20 years, while official inflation was 2%.
When you are middle class, those categories are around 70% of your budget. The declining price of cell phones and clothes don't offset the 1% more than inflation rise in food prices and 2-4% in rent/mortgages. And that share of one's budget going up faster than inflation is worse if you factor in taxes like property taxes.
But for the upper class, these sectors are a much smaller portion of their budget, so the cost increases don't matter as much. Whereas the middle class has to do what the BLS says and switch from steak to hamburger, chicken breast to thighs, and has a regular reminder of declining quality of life every grocery shopping trip or visit to the doctor.