It is generally true, due to a bunch of factors. Personally, I've observed 2 factors:

1. a lot of culinary tradition was lost by the boomers and their parents due to the advent of mass-produced, packaged food and the Great Depression. A lot of very basic, holistic techniques like making broth, rendering fat, became less common as magazine recipes, refrigeration, and boxed food encouraged discrete "buy x y z for recipe A" instead of having an assortment of preserved veggies/meats, broth, lard from previous days etc, to work with and learn from. I was genuinely confused to find my dad had to teach himself a lot of it in his 20s and my mom never learned.

2. Economic/cultural history. A lot of families didn't see making food better as worth sparing any effort or time on. My grandma's boiled veggies and potatoes, no seasoning, and meat fried in a pan, no sesoning, eaten and cleaned up as quickly as possible come to mind.