I think most people just want to outsource their thinking to someone else. It's easy to parrot the line than it is to question and assess for yourself - many people either can't or won't do that.
It always strikes me as strange as how the government is seen to get it so right on matters of things like road safety, which we are not supposed to question because going over the limit might be "unsafe". And get it so wrong on things like the performance of the NHS, which we are supposedly allowed to.
I think the 70 mph limit is pretty arbitrary. It came in in the 60s and hasn't really been revised since. I suspect there is a lot of statistical backing for why limits in general are necessary, but much less so for why it should be 65, 70, 75 or even 80 mph limit on motorways. Car safety has changed a lot over the years. ABS brakes, crash testing and airbags. Cars are much stronger and more stable. Roads are probably better surfaced and more well lit, and we are better at identifying accident blackspots and dealing with them.
OTOH the numbers of cars on the road have increased considerably and the reaction times and experience of people on the roads has probably changed. We probably see higher temperatures, so more rain and less snow and ice/melt transistions which to me are very dangerous.
Sometimes I see the government making good and significant changes that will impact road safety in what I believe is a positive way. Sometimes I see obvious stuff that they could do that I believe would make a good impact, but for whatever reason they won't or can't. And then I see other stuff like smart motorways that just seems like a recipe for disaster. The key takeaway for me is that their performance on this varies, pretty much like with everything else.