Why would reliability be relaxed? Other than just being silly on the face of it reliability is still important in cargo. It's even more important in the perception of aviation.
For the same reason we don't cover cars in 3" thick steel armor. It's still very important–planes and cargo are expensive. But overall cost might be optimized without quite as many zeros.
This is why old planes long since retired from passenger service are now used for cargo flights, which have an 8x higher accident rate. https://www.npr.org/templates/story/story.php?storyId=212692...