What do you mean with ‘it integrates’? It’s just the discovery feature of the App Store tied into Maps. Apple will use your location to give you relevant travel apps which you may want to use instead. Google can’t really do that, since it doesn’t control the App Store and also because it provides, in my case pretty accurate, public transport data itself.
When you search for something in Apple Maps, you can choose to switch to transit directions. Apple Maps then gives you a list of options to choose from. In my case, I have about 3 pure transit apps installed plus Google Maps. The local transit options are far more accurate and up to date than Google Maps.
The nice thing with Apple Maps is that you just click on "Route" for the 3rd party app you want to use and it seamlessly picks up from the location data you already entered in Apple Maps.
Try doing that with Google Maps. You can't. You are forced to use Google's crappy transit solution rather than the more accurate and up to date one made for your particular city. Or you have to just open your transit app directly and then enter the data all over again you already entered in Google Maps.
Apple Maps just provides more options and a more seamless way to get good transit information directly from local providers. Google Maps doesn't provide any choice at all except for their own inferior solution. Transit directions is one of the main reasons I dropped Google Maps.