It's worth noting that, long ago, clinchers were generally hookless. Safety was ensured by not running high pressures; that most clincher tires were thick and stiff possibly also helped.

The main transition happened in the 1970s, probably encouraged by the wake of the US bike boom, and its massive spike of clincher-equipped road bikes.
A few cheap tires still come with colorful "HIGH PRESSURE" labels on their sidewalls, a cheery throwback and a grim omen that they'll roll like a sack of potatoes no matter how they're pumped.