Well, in fact you do need a certain obedience from your new hires.
It's a bit optimistic to believe that every choice a team makes is 100% rational. Choice of a certain technology, coding language, coding style, management methodology, all these things are fairly cultural in the sense that people tend to push for things they're more confortable with.
My point is that integrating 2 teams of people where each group has a strong culture is a hard thing to do. It's really natural to form camps.
For instance, you're the cto of your company, and one of your principle is to limit your dependency on third party components. And you hire a team, where their culture is to build quickly on a lot of 3rd party libraries.
Nobody's fundamentally right or wrong, but the new hires will think that "we've joined this super controlling company that ties our hands and we can't do shit". And the cto will think: "crap we've hired this team of cowboys who will add a lot of operational risk to our processes".
And in a meeting where you try to explain your principles, it's way harder to impose your culture when you're fighting 10 people than if you fight 1 person.