It was never a problem before or 'back in the day', but a couple of things have happened along the way. And flat tappet discussion includes ALL motors, nothing unique about an FE in this regard.
1. EPA mandates for emission controls removed a critical additive to modern engine oils, virtually ALL modern engine oils. I think it was ZDDP, also known by other names. This additive directly relates to cam/flat tappet
oil starvation problems, especially during break in.
2. Cam profile/design has become increasingly 'radical' as to lift and duration. What we today might consider a 'mild' grind was a pretty hot setup 'back in the day'. With these new designs valve spring pressure went up, increasing the risk of failure for the cam.
This is an industry wide problem and when it first came to the attention of the major cam grinders most folks blamed it on inferior quality metals. Now we know it's the
oil (#1) thats changed, not the cam blanks.