Because Google is playing catch up and needs to pay higher salaries to poach from MSFT and AMZN and also pay much more for infra than what Amazon paid for theirs initially.
They don't need to "catch up" on infra. They need to catch up on their product offering.
they regularly deprecate old API versions in favour of new ones, which are not backwards compatible and usually more expensive
any time Google Cloud APIs change you have to update your code
and they break stuff, introduce bugs more often that you'd expect and prioritize new features over fixes (see bugtracker for confirmation)
this is why i'm never again touching GCP
They also might be building more actual datacenters and doing so in a high end / environmentally friendly way whereas perhaps Amazon has already done a lot of those investments in previous years?
Amazon and Microsoft both do that as well.
I have heard people claim that Amazon pays more and by that they mean that if you hold your Amazon stock until vesting, it appreciates so much that it ends up being worth more than whatever the Google grant would have been worth. But then you have to ask if the relative performance of the stocks will remain stable over time despite having changed recently, and factor in differences in employee churn and so on.
that $350k base limit is top of the band, not everyone walking inside the door is going to get that. A friend of mind got an offer from AWS about a month ago, his base was offered $180k