You reach a settlement instead of a judge deciding a court case if both sides agree that a settlement is better for them than paying court costs, lawyers cost, the risk of losing, having embarrassing details published, distraction for a business, waste of time, and the stress of a court case.
If the plaintiff wants to be able to publish details of the case, there is a lot less reason for the defendant to enter a settlement agreement.
You complain that third parties miss out on possible information. That’s exactly why it isn’t there, because the defendant doesn’t want it to be there.
The defendant might offer “I’ll give you $ 1,000 if you agree not to say a word about the case.” If the plaintiff says “I want $ 1,000 and tell the world about what happened”, then the defendant will likely say “take our offer, or take us to court and our lawyers will do their best so you get nothing”. The defendant will just not offer the kind of settlement you are looking for. And the plaintiff will do what is best for them, not what is best for anyone else.
You have to remember that a settlement cannot be forced upon both sides, it must be something that both sides agree on. It's easiest to agree if you give the other side what they want if it doesn't cost you much, and then get things that you value more in return. As a plaintiff, not telling the world about the case is something that costs me nothing, but may have high value for the defendent. On the other hand, I value cash from the defendent a lot, while the defendent may be rich and can easily afford it. Because both sides have to agree, the terms are likely to incorporate something that both sides want.