It is a competition to see who can crack the most eggs. Anybody can do it, but the winner is who is willing to spend the most time doing it.
Google, and any commercial non-hacking organization, just has very little incentive to really waste a lot of money on that task. Where as basically every military and law enforcement arm of the US government has a ton of incentive and boatloads of money to spend cracking eggs. The military arms certainly spend billions a year and it would be quite unexpected if the law enforcement arms are not each, individually, spending hundreds of millions to billions per year.
Is the quality lower? Maybe. But exploit development is so easy that hardly matters. If you want to hack somebody then good enough is enough.
For that matter, who do you think hired various domestic hackers out of jail?
At this point, the advantages of exploit development are so obvious and lopsided that you need evidence that an agency with motive is not engaging in exploit development. Even then, they routinely lean on the other agencies to get access to hacking capabilities that they might not have in-house, so the gap is even smaller if we talk about hacking capabilities.
[1] https://www.justice.gov/opa/pr/us-department-justice-disrupt...