Why do you automatically assume it was corruption?

More than likely, it was just a poor job by some junior examiner.

I never understand why people are so surprised that the PTO screws up so often. They are a giant bureaucracy that has to handle a really complex job.

There are multiple processes available to kill this patent (reexamination, post-grant review, inter partes review). However, they are all fairly expensive.

We are talking the government here. Mistake happen. If we are gutting the government for incompetence, the PTO is really not my top concern.