Entrenched economic interests
Their were not such powerful economic interests blocking the mass adoption of those new technologies in the early 20th century - no giant horse-breeding companies or multinational buggy building corporations. The huge technological advances of that era spawned the most profitable businesses that the world has ever seen, with power that rivals or exceeds that of governments. These corporations strenuously resist the replacement of the technologies they are built on by the next big thing. This is a major reason why innovation has had limited impact on many areas of our lives.
As for flying cars - an air traffic control nightmare. It's human pilots that are holding that back, it will only work when computers take over the flying completely.
