I'm seeing my own costs, for a site which I run on my own, rise from $1,500 / month to around $30,000 / month.
Their rationale is essentially that they did not want commercial users abusing their free tier. Before this change, they had been reaching out to such entities individually, offering their 'premium plan' service.
The pricing for the (old) premium plan was remarkably similar to the new pricing which now applies to everyone.
This pricing change has ended the era of Google Maps mashups / hobby projects.