The incognito trick has nothing to do with the Googlebot. Sites can definitively know the Googlebot by its IP, and Google doesn't care about if other visitors with no referrer see a paywall. The probably reason the New York Times doesn't use a more comprehensive paywall is that those generally have failure modes like accidentally blocking humans who haven't been on your site before. Sites like the New York Times have weak paywalls to be user-friendly, not because it's required by Google.
It doesn't have anything to do with Googlebot, it has to do with Google's "ghosting" rules: You can't have inaccessible pages be indexed, you need to permit visitors X views free per day/month.
