One thing people hate to do the most is learn something new. You have a bunch of engineers who already know ins and outs of AWS. Your stuff _works_. Would you consider moving it elsewhere? I didn't think so. Now consider that there are literally thousands of ISVs offering their stuff there, for whom porting to GCP means hiring more people, increasing complexity of the product (so that it could run everywhere), etc. Why would they pick GCP instead of e.g. Azure, which has _insane_ level of sales access to enterprise accounts?
I'm a big fan of AWS, but I purposely avoid using too many AWS services that would lead to me being locked in and able to move if I wanted to. Porting deployment scripts to another API isn't too hard, but having to build and support my own replacement to SQS or DynamoDB (and then port my services to the replacement system) adds a lot more to my costs
It was a much different situation with G+ vs FB -- Google was trying to compete for (often irrational) customers and had to convince customers to make the switch to a new social network when they already have a perfect usable social network that costs them nothing that Mom and Dad and the kids are already using so everyone is already there. There's a lot of friction in changing social networks since in order for it to he usable, not only do you need to switch but all of your friends and relatives have to switch too. In comparison, porting code to new API is much easier than getting Aunt Bessie to post her cat pictures on G+ instead of FB.
You can compete against a paid product with lower prices, but you can't compete against a free product with more free, you have to show real value, and G+ just doesn't offer that much value over FB for most users.