The issue with Powerful Build is that it doesn't really change playstyle or the feel of a character. A human vs an orc with Powerful Build (both with +2 Str) would play nearly the exact same way, particularly so in combat. Especially since carry capacity is so easily negated by having a party and/or getting a Bag of Holding.
If Powerful Build affected Shoves or Grapples or Melee attacks or Athletics Checks in general in a meaningful way, that'd be different. But as is, Powerful Build isn't really an appropriate replacement for +2 Str (and this ignores the fact that Orcs already had PB along with +2 Str, and so the dedicated +2 Str ASI wasn't actually replaced with anything). Mechanically, an Orc can't do any of those listed things better than a human or gnome.
There's more to Powerful Build than just carrying equipment. It probably varies a lot by table and how often these things come up, but it also lets you do things like pick up heavy objects, NPCs (once you have them in a grapple), push or pull heavy objects, etc. It's a utility feature more than a raw combat feature. You can sack STR and still be able to pick up guys by the throat, and if you don't sack STR you end up being able to do stuff like picking up a wagon and holding it overhead.
Which is fine. Not every racial needs to be combat oriented. There's more to how a character plays than how they perform in combat. And the goal of racial abilities isn't to perfectly replicate the benefits of the attribute bonus. If it did it'd defeat the point of removing ASI from race. The point is to just make sure the races feel different in play.
All that said, I'm pretty sure 5e's rules for grappling and throwing things were written without Powerful Build in mind. One DnD should ideally take a look at some of those old mechanics and factor in weight vs carry capacity rather than raw STR to better integrate the feature into the system.
Edit: OH. I also forgot to mention. Powerful Build gives you advantage on escaping the grapple condition as of the UA that added Goliath to OneDnD's PHB. So the trait is getting buffed.
