You could ask this question of the original Half-Life, but not of Black Mesa. In my opinion, one of the greatest improvements for immersion is giving those NPCs situational dialogue and reasons for why they won’t follow you. It sure as hell beats Half-Life’s deadpan drones who do what you’re told and, when left alone, will stand upright until they keel over from hunger.
Every time I had to leave NPCs behind, the developers thought to give them a few lines to explain why. “Yeah, no offence, Doc, but I’ll find another way that doesn’t involve swimming through shit n’ leeches.” That’s all it takes, really, and I’m glad they did it. It gives the NPCs a point insomuch as any extra in a survival horror movie has a point, and it makes it feel like these guys will do what they can to survive if I’m not there to tell them where to stand.
Aces on that part.