Well, quite simply... the Bible does not hold all answers. It is first and foremost a work on salvation. It is also compilation of documents relating to one particular narrative of salvation. The Bible is a historical work, an archival work, a work of literature, and many other things.
It does not explain the workings of say the reproduction of pine trees. It won't help me with differential equations. It is very lacking as a source of mechanical knowledge. But that is not the object of the Bible.
So, if the object of the Bible is to teach salvation, and it does not explicitly state the trinity, then explicit statement of the trinity is probably not necessary for salvation. What is necessary, it would seem, is understanding that God exists, Jesus is the son of God, and the Holy spirit is imparted from the Father to Jesus to us. That this faith as well as the fruit it bears are necessary. It is likely many believers would go on to say, aha, this is the trinity... But it is the substance, not the token, that matters.