As to ease your worry here a little, any launched cloud products have at a minimum a 1-year deprecation policy[0]. Anecdotal: AppEngine deprecated their Master/Slave datastore[1] in April 2012, and it was actually shutdown on July 6, 2015. So that's 3+ years to move to newer tech.
[0] https://cloud.google.com/terms/ (section 7.2)
[1] http://googleappengine.blogspot.com/2012/04/masterslave-data...
You point out examples of longer deprecation, but that doesn't matter one iota to people evaluating the cloud. Track record isn't legally binding, unlike the contractual 12 months.
[1]: http://www.networkworld.com/article/3029164/cloud-computing/...
[2]: http://www.recode.net/2016/4/28/11586526/aws-cloud-revenue-g...
3. They gave you more than 3 years :)
Google is very committed to GCP and you see it in their work. Much like Amazon, they have a huge sum of computing capacity they aren't always using. It's an obvious business play.
But what's more, it's become the basis of differentiating their mobile platform. Google is trying to develop and sell-for-cheap the tools to make really good mobile apps (e.g., Firebase) to try and shore up the app ecosystem of their platform.
Given that a lot of the things they offer are 3rd gen variants of their core tech for developing things internally, it seems fairly reasonable to assume they're in this for the long haul.
Digital Ocean and AWS are dedicated to continuing this line of business and keeping those customers addicted. Google is conducting another large and expensive moon shot which fine since it's part of their DNA.
I'm not sure you can say it is an expensive moonshot at this point.
I'm not using them, myself, but I wouldn't consider that aspect of the risk substantial given the fact that I could erect identical infrastructure on AWS in the worst case scenario. And I have had to plan exit scenarios from AWS because ultimately they're a single vendor with arbitrary control over their platform, as well.
GOOG/Alphabet as a company is going to be around, but will this line of business be with this set of offerings?
So you're advocating we should trust the book vendor?
That's why GCE should be as important to Google as AWS is to Amazon while arguably both have a different "core business".
AWS is there through first-to-market leadership.
Microsoft is there because they've got a strong sense of what every SME and Enterprise customer in the world wants.
Google are there because they have deep expertise in building these kinds of systems and it would be utterly bonkers not to try and diversify into this field.