What Makes a New Testament Manuscript Trustworthy, Accurate, and Weighty?

What is it that makes P66 P75 א B ‘quality external evidence’ or very weighty evidence over A* Θ Ψ 050 f1, Maj? Maj refers minuscules The Majority Text; that is, a group that is made up of thousands of minuscules that display a similar text. So, here we see that counting the manuscripts (the majority wins) does not mean that the majority is evidence for the preferred reading being original.