Well, apart from the OEM violating the Android Compatibility Definition Document (CDD), failing the Compatibility Test Suite (CTS) and thus not getting their device Play-certified (so not being able to preload all the Google services, there is an economical impact as well:

As OEM you want Carriers to sell your device above everything else, because they are able to sell large volumes.

Carriers make money using network traffic, Google is paying Revenue-Share for ads to Carriers (and OEMs of certain size). Carriers measure this as part of the average revenue per user (ARPU).

--> The device would be designed to create less ARPU for the Carrier and Google and thus be less attractive for the entire ecosystem.