The idea is that if there is an electrical fire it will spread out via the holes in the wall. Fire resistant enclosures are meant to give you time by containing the fire in the wall longer. PLA will not only melt immediately but it will also catch fire and fall to the ground. This will reduce the time you have to safely exit your home. Due to the prevalence of plastics in modern homes you’ve already got very little time even in a code compliant home.
The idea is that if there is an electrical fire it will spread out via the holes in the wall. Fire resistant enclosures are meant to give you time by containing the fire in the wall longer. PLA will not only melt immediately but it will also catch fire and fall to the ground. This will reduce the time you have to safely exit your home. Due to the prevalence of plastics in modern homes you’ve already got very little time even in a code compliant home.