because marines are apparently idiots
I comm alot of games, and the most annoying thing possible is to have an ideal build utterly screwed over because your marines refuse to build structures you've dropped even while you yell at them. In NS timing in res usage matters. "hey comm, I'm in the hive, drop me a PG" "YOU RAN OUT OF BASE WITHOUT BUILDING THE OBS YOU MORON!", happens to me at least every second game these days. If you don't know how to comm, then listen to the comm, because he's responsible for knowing how to win the game, not you.
Now, in a game of NS you should know that good comms drop structures on the far wall away from the comm chair. This is a good place to start when the comm asks you to build something as soon as you spawn. Browse the far wall for structures that need to be built. Hopefully you've been playing long enough to know what an unbuilt structure looks like at a glance. This leads to part 2... If you still can't find it start looking at other places, other walls. Especially obs sometimes get placed in different places to take advantage of their view radius. Look close to the entrances of bases. If you have looked around and can't find the structure you were asked to build, this is NOT an invitation to leave base without building it. The extra 10 seconds it takes you to ask the comm where the structure is are better used doing that then running towards the aliens first hive and dying uselessly again. Although I know how much all you 1337 players love to do that. It's possible that you misheard the comm, or you were expecting to build a different structure then was actually asked to be built. Check the dropped structures and make sure they are all finished. Especially IP's can be hard to see.
Overall, just for the love of God stop running out of base like a superhero when I'm yelling at you to build my damn obs. If the obs goes up late that means phase goes up late, and I can't set the siege up at the second hive, and therefore we lose, just because you didn't obey your damn orders the first time. Promptly building a structure after it is dropped massively improves the comm's build efficentcy and means in the long run you're probably alot more likely to win. Plus I'm a nice guy, if you're a good player and you waste time building for me, I'll probably drop you a shotgun or HMG. It's worth it.