Honestly I think they care about home brew world building.The kind of questions being discussed, eg: whether fear effects are magical or not, halflings place in worldbuilding etc are fundamentally unanswerable in 5e.
It's clear that WotC simply does not care about worldbuilding. It's not a priority of 5th edition at all.
What they obviously do care about is whether something is cool or fun in a game.
That may be an issue for those of us who care about worldbuilding, but clearly this is not an accident of design. They may have made the Forgotten Realms the default world, but at no point have they ever, even for a moment, appeared to let that constrain them in what options they put before player characters.
Is Dragonfear a magical effect? You'll have to decide yourself. The game doesn't care.
If Halfling luck an inherent quality of the halfling species or just a thing halfling characters have? You'll have to decide yourself. The game doesn't care.
How do halfling societies interact with their neighbours. You'll have to decide yourself. The game doesn't care.
You can criticise a company for making a hammer, when you would have preferred a screwdriver, but it's a bit silly to be criticisng a hammer for being bad at screwing in a Phillips head screw.
”A world of your own” is the title of the first chapter in the DM guide.
They encourage many assumption on world building, and wisely they don’t restraint DM with racial tight definition or demographic system. Stating That halfling are all lucky is good for some world building assumption, not for all.