I misread your original post , I apologise. You have to remember that each team has their own vision and interpretation of what Black Mesa and its inhabitants should look and feel like. If the BM devs gave permission for Tripwire to use their assets in OBM and GD then I wouldn’t have any problems with it. If they just waited until BM released and essentially stole their assets to cut corners on their own mod, then that would probably piss alot of people off.
Also, how much consistency are you expecting? Should all the enemies be the same models across all 3 games? Should they all use the same weapon models and sounds? Looking at GD and OBM now, I’d say they already look pretty consistent with BM, like they’re all one cohesive facility. It seems like they have their own direction for the expansions, and they might not want to compromise on their artistic integrity for the sake of using another teams assets.