Because Pixar is a big company, security and reliability are crucial. Pixar uses Workstation-class and HEDT PCs that are built on Xeon or Threadripper CPUs, Nvidia Quadro GPUs, and ample RAM.
Last we heard a typical PC Consisted of a 16-Core 2,3GHz Intel Xeon CPU, 64-128 GB of RAM and an Nvidia Quadro M6000 GPU. Chances are these specs have been upgraded already over time, though.