This generalization is very misleading. Many national parks are massive, with vast tracts that can only be reached by days of hiking or an off road vehicle or an aircraft. This is true even of extremely popular parks like the Grand Canyon, Yosemite, Zion, Joshua tree, Smokey Mountains, and Denali.
The Yosemite valley in summer for example can feel like Disney in terms of crowds, but that is just a small area of the park’s land. The entire eastern part of the park is far less busy even along the roads, there are plenty of remote trails for backpacking, and then there are true wild spaces without any official development.
The national parks offer a range of natural experiences that can suit almost everyone.