I have never had an electroytic capacitor failure in the field???

Electroytic are the least solid state compenent of solid state. Electroytics have a finite life. They very common failure item.
ESR is more of a concern in switching suppies. And it can cause heating in the caps. If they get hot enough to fail that is poor design. The EE is supposed to keep them cool enough to last for the "design life".

I think the plastic is supposed to provide electrical insulation, not thermal. Mallory or Sprage used to print on the case. Then they put clear sleeving over it