No, I feel pretty clear about the reason.
A very large portion of the openly presented argument against the LTN principle is the idea that it displaces traffic and pollution. On this specific point, there is agreement that things improve (pollution-wise) for those inside the LTN.
There is disagreement about the consequences for streets around the LTN, with opponents claiming that things here become unacceptably worse, and supporters claiming that the effects are small, and/or temporary, and are outweighed by the larger benefits.
Because those who support the LTNs are the ones that want to make a change from the status quo, they are put in this position of defending possible negative effects of making a change. They can talk all they wish about the current, ongoing negative consequences of not doing anything, but the anti-LTN side can avoid being held responsible for that because hey, they aren't suggesting changing anything, and it's for someone else to come up with alternative solutions.
Well, if the anti LTN side really believes that there's an overall benefit of maintaining things as they are; that is, traffic should not be concentrated on main roads but be allowed to disperse freely as it wishes, then there should be no objection to widening that strategy so that more people can benefit from it. Any existing measures which are designed to keep traffic on main roads are already causing harm, so these measures should be removed.
The purpose of asking the question "ok should we remove historical LTNs" is to put the anti side in the position of defending and justifying an active intervention that follows their claimed principles and beliefs.
Of course an anti LTN person doesn't want to be put in the position where they have to advocate something that will directly increase traffic and pollution on someone's street. Of course they don't want to become answerable to those people. That would require full courage in their convictions, and I don't believe they have it. If they did, they would prove it by being happy to advocate removing long-existing restrictions.
Speaking for myself - but I think this would apply to most people who are basically in favour of the LTNs - I do have the courage of my convictions. It might be that I am wrong, but I do genuinely believe that LTN type strategies are part of what needs to be done to reduce the problems that traffic creates. It is never easy when you are confronted with someone who tells you that they live on a main road, and they believe pollution has increased as a result. I am able in most cases to say to those people that I genuinely believe that pursuing the LTNs will in the long term make things better or at least no worse for them.
If those who oppose LTNs on the basis that they unfairly displace pollution to main roads really believe that, then their rationale should apply to LTNs whether they were put in place in 2020 or 1970. I would stop short of saying that all those who use this argument are doing so disingenuously (although I think some certainly are). I think there are probably lots of people for whom it's a genuine worry, but they may not be willing to examine the thinking behind it. Either way, the result is that whenever this question is asked, it is avoided.
