For me, three reasons:
1) Never had a problem with a P-N barrel but have with Krieger. And I do realize that some can say the exact opposite.
2) Turnkey re-barreling. And coating now too.
3) Barrel contours. I don't believe Kreiger is as flexible especially with lightweight contours.
And from what I've seen the same thing can be said about most any pair of barrel makers you name.
