I feel like Barney’s voice was scrapped from Blue Shift, you can definitely tell that Barney speaks to Rosenberg and others, and in the trailer, he also speaks. So Game Theory here! Barney actually had a voice but Valve decided to scrap it to fit the Half-Life theme
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Not sure about this. Same scenarios occurs in Opposing Force when the npc asks you things. It is part of the series' style that the character doesn't speak and so they wanted to continue that. Also Blue Shift wasn't made by Valve - Gearbox made it.
Gearbox is a bunch of gears in a box, they forgot to ask Michael Shapiro for more lines and didn't want to splice or use assets again.