You used to see it a lot more often - now you only see it occasionally (see Mike Blumenthal's 2015 blog post for more info. I've chatted a few times with the AdWords folks at Google about it and got the scoop.
They are now a form of "endorsements" (see https://support.google.com/accounts/answer/3403513) and they are sort of like Wright whales, Florida panthers, and Barton Springs salamanders (sorry, had to work in an Austin reference somehow) and other endangered species that were never rare in the best of times. Local phone numbers, hours of operation, and direction links all have a higher relevance priority and so bump the endorsement extension out of the ad. In rare circumstances - an AdWords Express account with a suspended GMB account, and deleted hours-of-operation, etc. - they will still pop up.
Want a real unicorn? Try finding a PURE shared endorsement. They still exist - saw one for a donut shop in Johannesburg last month.
New advertising option:
A review of your product or service posted by a Sterling Sky employee. This will also be shared on the Sterling Sky & LSF Twitter accounts, our Facebook group, LinkedIn, and both newsletters.