Considering how many millions Netflix pays Amazon every single month, a team of highly skilled engineers is a drop in the bucket, and if switching means they can save enough, they'll do it.
"The closing of Netflix’s last data center has been seven years in the making."
Does that sound like a drop in the bucket?
Compared to the running cost of their streaming service, yes. Besides, I like to believe (yes believe, because non of us outside of Netflix would be able to verify) that they've spend that much time such that they're far less dependent on the underlying architecture.