The decline of patriotism is the result of a long, coordinated attack by Marxist intellectuals. After igniting their attack on Western values in the 19th century through communist economic theories, they shifted in the 20th century to cultural Marxism by dividing society along racial and gender lines. This culminated in generations of children learning to hate American history, traditions, and ancestry. American pride is lost because those in charge of teaching history hate America.
There certainly has been a decades-long attack on the country, but corporate conservatives, not the left, are behind the scheme. Following historic policies banning child labor, raising minimum wages, and passing civil rights laws, the corporate donor class began offering voters a false sense of nostalgia for the 'good old days' while secretly pushing for policies that rob the middle class to make the rich richer. Patriotism is the love of America and its history of progress, not of the 1%.