They could've had e.g. "Windows Fresh" campaign/symbol for vendors to use if it was an unmodified Windows. But there's likely no incentive. It cuts into OEM profit, and maybe it would reduce support calls?
Ultimately though, most people don't care. And the ones that do simply reinstall Windows on a new PC, because it's quicker that way.
Microsoft hates McAfee and the other malware packages, because they know full well how badly they screw up all sorts of internal workings of Windows. Much of Microsoft's own tech support workload is caused by shitty antiviruses. The reason Microsoft made Security Essentials / Defender was to deal with that, to displace the others and reduce Microsoft's own support workload.
Candy Crush isn't anything like that, it doesn't screw up OS functionality. (Well, subjectively, you might consider ads and upsells in the UI broken.)