I think they did have ejection seats for the first couple of flights. For the first launch the body flap was bent back beyond design limits from the pressure wave of the solid rockets igniting. John Young said if he would have known what happened at the time, he would have ordered an ejection. Such a mishap should have made the Orbiter uncontrollable on reentry, but obviously they made it.
Had management taken the Columbia foam impact seriously, Shuttle Atlantis was already on the launch pad and could have done a rescue.
It's hard to take a foam impact seriously.
Thinking of it as a foam impact rather than a foam-reinforced ice block impact militated strongly against a generation raised on Nerf guns and Nerf bats worrying much about it.
IIRC, it wasn’t a seat. It was a boom that deployed out 40(?) or so feet from the hatch. the astronauts were supposed to get unbuckled, stand up against any acceleration forces, clip a ring onto this rod and slide away and off the rod past the exhaust plume, free fall, and deploy parachutes...