In the very first missions with only two astronauts, the shuttle had ejection seats. They were removed when more than two people flew at a time, because a) it is not possible to add more, and b) crew ride on two decks, not one.

After the loss of Challenger serious consideration was given to designing some sort of escape capsule for the entire crew, but it was decided that the weight and practicality considerations were not worth it.

The bottom line is that it is impossible to design any practical means of high-speed travel that can cover all eventualities. A century of extensive experience has led to air travel being the safest way to travel on average, but there are still fatalities. Maybe once we have a century of experience with Starship and its descendants we'll be able to say the same about space travel.

But we were in a hurry, so it was just part of the project.

https://airandspace.si.edu/collection-objects/crew-escape-sy...