Unless the service is monstrous like search or GMail, working on maintaining existing product infrastructure is a career dead end in the company, the game is to

Unless the service is monstrous like search or GMail, working on maintaining existing product infrastructure is a career dead end in the company, the game is to be part of a project launch. And Google's back end stuff constantly changes, so significant amount of maintenance is needed to keep anything running indefinitely, another reason for all the things they've killed. Maybe the conversion of Nest's infrastructure was internally viewed as more maintenance than new project, so it didn't get much in the way of resources? Google palpably doesn't care about brand damage so that's not a consideration.