I think the popularity of the ancient machine families on both GCE and EC2 is due to inertia and copypasta and ignorance. People write down "m4.large" and just leave it that way until it stops working. The GCE N1 family that contains SNB and IVB is slower but not cheaper.
That's a good point. I was thinking more about from GCE/AWS side, they'll keep these old machines running because they can shuffle off low priority/power loads to them. But it makes sense from the customer side they're just configuring by rote rather than looking for the best price-performance.
https://miro.medium.com/v2/1*j7PlMPFDlWI78cMdENJh7Q.png