It's the tyranny of the rocket equation. The more mass you add, the more fuel you need to reach orbit. But that fuel also has mass, so you need even more fuel to lift the fuel you've just added, as well as bigger tanks- adding even more mass...

To maximize the amount of actually useful stuff in space (the satellites) you want to make the rocket as light as possible. Adding an ejection system would add significant mass as it would have to take the satellites, the payload adapter and the fairings, separate them from the rest of the rocket, parachute them back to Earth and then survive out in the ocean for several hours (most launches are over water to prevent you from hitting someone in cases like this) until they can be recovered.

And that's on top of the extra cost and complexity such as system would add. Since non-organic payloads can readily be rebuilt, it's just not worth it.