It would be no skin of Google’s back to multiply these bug bounties by 10, and they should.
Why's that? It's not retirement money. 400k (salary+stock) is one year of compensation for some Google engineers.
And very, very few Google engineers make that kind of money.
You'd be surprised. In Mountain View, everyone level 6 or above makes at least that amount, and most level 5s probably do as well. I'd guess that probably 20% of engineers are T5 or above, which is a ton of people when you multiply by tens of thousands of engineers.