Why measure Page Authority (PA) instead of Trust Flow (TF) in web2.0s?

For web 2.0's, we measure Moz PA (Page Authority) and offer PA of 20 or greater.

WE DO NOT measure TF like we do with domains. Why? Majestic measures domains accurately for Trust Flow BUT does not for Web 2.0's which are built off a main domain rather than stand-alone root domain. Hence, we use Moz PA of 20 or greater to measure the quality of Web 2.0's.