I think the real problem is that the patent office gets fees for approving patents, and no negative feedback for approving bad ones. The natural result is that they externalize the cost of disproving bad patents to the population at large. Do the people who approve overturned patents even hear that they've been overturned? If not, then there's not even the emotional cost of being told they've done a bad job.

If whenever a patent was overturned, the Patent Office had to pay the court costs of the one who managed to overturn it, they'd be a lot more circumspect about what they approved.