While it was always a concern, it was not a practical concern.
It would not be reasonable to require an 1970s satellite launch to be able to clear out the debris if the satellite exploded after a collision, because that's something we aren't able to do even now, 50 years later (note that the proposal is for 'thinning out', not clearing it). So obviously it was acceptable for companies to throw their junk without having a plan in to place to remove the debris after an accident - they are required to have a plan to deorbit after a normal operation, since that is actually a reasonably practical requirement.
Stating that this is unacceptable would mean that essentially no satellite launches would happen, and so the society chose to explicitly accept launches without a responsibility for clearing out the debris.
It would not be reasonable to require an 1970s satellite launch to be able to clear out the debris if the satellite exploded after a collision, because that's something we aren't able to do even now, 50 years later (note that the proposal is for 'thinning out', not clearing it). So obviously it was acceptable for companies to throw their junk without having a plan in to place to remove the debris after an accident - they are required to have a plan to deorbit after a normal operation, since that is actually a reasonably practical requirement.
Stating that this is unacceptable would mean that essentially no satellite launches would happen, and so the society chose to explicitly accept launches without a responsibility for clearing out the debris.