Power lines catching on fire a common occurrence in Vietnam?  

This is down to dated wiring and lack of maintenance. Yes, the hot weather will impact it but not this much. I think they need to work on rewiring a lot of areas to prevent it.

I've watched a few videos of this on YouTube.

I hope that's not a common occurrence anywhere. When I was in Vietnam, I remember seeing power lines overhead and wondering if it's safe walking underneath them. Some places have messy power lines. I hope Vietnam sorts this problem out.

I have seen this happen in other places. They likely just need to update and fix faulty wires. It is an easy fix but a lot of places just don't bother because it costs money. 

This is not likely common, it just happens in very densely populated areas. If the wires are neglected for several years, it is bound to happen. 

I have seen this happen in other countries. When you have dry hot air, it is bound to happen.

They should use coated wires to prevent this but this is down to the area to repair and replace them.