Also the numbers of patents are presented every year to prove, how grand the nation is. Nobody wants to spoil that.
(BTW: That would be a real patent reform)
Not exactly, the USPTO is funded by the patents it examines and keeps active (maintenance fees). Issuance fees are actually small compared to the rest of the fees involved in examination. Additionally an issuance happens only once, but rejections are unbounded. If making money was an incentive, they'd do much better by repeatedly rejecting applications and forcing applicants to keep paying for continued examination rather than issuing them.
But I don't think, that repeated rejections would make the patent office happier. First of all, they would create much (political) pressure from the big corporations and second if they reject to much, the number of patent applications would decrease.
Third, they would cash in less maintenance fees.
Maintenance fees are quite a bit higher, but they are bounded (only 3 times over the life of a patent). Also, they are not guaranteed, because often a patentee finds out that the patent is not worth much due to the vagaries of the market and abandons it. However, it would be interesting to model this as a maximization problem given enough statistics about the probabilities of applying, continuing prosecution and abandonment...
In any case, this is all academic because the PTO gets to keep only flat amount of the money it brings in. Everything extra goes back to the Fed. Money is really not an incentive for the PTO.