There were only 2 ejection seats, enough for the crew of test flights but not the larger crew of operational flights.
The seats were only installed in Enterprise (the prototype, used only for suborbital tests) and Columbia (only enabled for STS-1 through STS-4 test flights, disabled for STS-5 the first operational flight)
The seats would only work at low altitude and speed (I've seen differing numbers cited). For the Challenger disaster they would've theoretically been useful (ignoring all the other factors), but they would've been useless for Columbia due to speed.
And it's not clear ejection would have actually been successful with the SRBs still active and right there.
The seats were only installed in Enterprise (the prototype, used only for suborbital tests) and Columbia (only enabled for STS-1 through STS-4 test flights, disabled for STS-5 the first operational flight)
The seats would only work at low altitude and speed (I've seen differing numbers cited). For the Challenger disaster they would've theoretically been useful (ignoring all the other factors), but they would've been useless for Columbia due to speed.
And it's not clear ejection would have actually been successful with the SRBs still active and right there.