It's not really that, they use more or less the same design that high end GPUs have been using for years (decades?), it's just poor console design choices that made it happen. It's not that it was being put under too much stress, it's that the console wasn't properly designed to handle the normal every day stress (or late-term "push the console to the limits"-strees).
There are many factors that lead to it, lead-free solder certainly did not help, but it's essentially a requirement to sell their console in many countries. Not having proper standoffs like a PC (and the original Xbox), terrible cooling design (way too small of a heat sink for the GPU, which was basically a passive heat sink anyway how the fans are placed), having the GPU and CPU heatsinks mounted to the chassis. Bad choice after bad choice. This changed when they finally released the Jasper (45nm-based GPU) consoles in late 2008.