Another pylon observation

I've posted a lot about pylons because they are a very visible piece of Physics. I have been working on learning to see things. I have been to good at looking but not seeing. Things are so familiar that I don't notice details or changes. So it was that I finally spotted that the wires on these pylons are held up by double sets of insulators. Observations lead to questions. Is it because of the weight of the 4 wire parallel bundles? It can't just be that because I have since seen 4 wire bundles held by single insulators. Is it because it is 4 wire bundles over a longer distance and thus heavier? It might be, because I think the pylons were at 300m separation here. I will make further observations to see if I can come up with an answer.