In 1.13, pigmen kept aggroing newly spawned pigmen until you left the area (with for example a nether portal) and came back. This meant that pigmen were scary to the average player (as they should be), but not impossible to deal with.

However, in 1.14.3 pre-1 and possibly the other 1.14 versions, I think there was a bug where pigmen never deaggrored at all, even when leaving through a nether portal and coming back. This obviously would make them much harder to deal with, only making them deaggro when all affected pigmen despawn, which they won't do when leaving through a portal.

In 1.14.3 pre-2, you attempted to fix this back to 1.13. However, it seems that newly spawned pigmen won't aggro at all and if you hit a pigman, the rush of them will end too fast as no new ones are getting aggroed.

I believe this is a bug, and that the system should be reverted to the 1.13 system.