It's a very sad situation indeed.
Looks like (in the Florida accident) the guardrail hit the front left corner of the cab section, and then scraped along the left side. The article says he lost control and then struck the guardrail. There could be lots of causes of losing control. It does show how little extra structure there is in many RV walls (of most any RV class/type).
The Texas one may be one or both drivers going a bit fast across the narrow bridge, not expecting to meet another fairly wide vehicle there. Goodness knows it's plenty easy to do that sort of thing on roads where there's little traffic volume. We all need to be alert and to drive with due care for the situation; the results of doing otherwise can be terrible.