Google has an existing partnership with ADT for monitoring their Nest Secure product so I'm not even sure it's all about the install base. There's a lot of mutual benefits to that partnership, ADT has the existing network of people-oriented call centers and installation crew without great hardware & tech, whereas Google's tech is much better but without any of this timely & expensive infrastructure built out.
Google's products are also expensive. The Nest smoke detectors are priced to only be viable for a studio apartment. Beyond that, you're way better off going with a traditional alarm/fire system.
Requirements are 1 in each bedroom and 1 in the hallway outside each bedroom. That adds up quickly.
The alarm.com smoke detectors are $50 and also last 10 years. You're paying a lot for a Google badge that doesn't even contact the fire department with the base setup.
When a smoke detector goes off, I've got my system set to:
1) Turn off HVAC/heat
2) Unlock exterior doors
3) Turn on lights
4) Flush syncs of any local data to remote sources
What's the google price tag for again? Initially it was worthwhile for the panicky waving motion to cancel alarms. But then they removed that.