cf doesn't conduct heat as well as alloy, if the brake tracks get hot due to extreme conditions and/or bad technique then the inside rim wall can become hot enough to cause a latex tube to fail (even a butyl one if things get really bad)
some people manage to overheat their cf rims to the point the resin softens and the rim distorts, this is far above the temperature at which a latex tube will fail
alloy rims have much higher thermal conductivity, the rest of the rim acts as heatsink to help cool the brake track
Enve describe their logic well here. https://enve.zendesk.com/hc/en-us/artic ... her-Wheels
It's not about the heat tolerance, their view is that it's an inconsistent material to manufacture from.