For Web 2.0's, why do you measure PA and NOT TF?

Why we do NOT measure TF (Majestic Trust Flow) for Web 2.0 properties? TF is a good measurement of domain quality for PBN's and measuring competitors site strength. It is NOT a good measurement for Web 2.0 proprieties that host hundreds of thousands of sub-domains thus we use Moz PA (Page Authority) to measure the quality of Web 2.0's. Anything above a PA of 20 is considered good quality for back linking purposes.

TF is good measurement for domains like money site and PBN's.

PA is good measurement for Web 2.0's which often have hundreds of thousands of sub-domains.