The campaign continues

Yesterday was the second session of my new D&D campaign.

The heroes had just found a lost city of giants , living in solitude underground for several thousands of years. They are taken to the giant king, who explains that his people have hidden themselves, awaiting prophecy and the one they call the 'world shaper'. But they might soon become discovered. Some of their youths went on a coming of age quest to the nearby temple of Maitri and they still haven't returned.
Determined that these youths are the ogres attacking the village, the heroes set out to stop them. They journey to the temple and confront the ogres in combat. They kill them but are now themselves trapped in the ceremony, unable to leave it until it is complete. They journey through caves to find the guardian who must part words of wisdom to complete the ceremony. But they find the guardian missing and an evil looking frost salamander in his place. They manage to defeat it and find a gem hidden in the carcass. The gem has strange magical properties.
The heroes head back to the giants to tell them of the unfortunate fates of their youths. For some reason the dwarven cleric accompanying them has vanished while they slept in the giant stronghold. They move on to the village of Smallbank to sell their spoils of war. After selling the mysterious gem to the local magic shop, they receive a new companion, a favored soul to compensate for the loss of their cleric. A loud bang is heard and when the heroes rush to the scene, the magic shop is destroyed and the frost salamander has returned. They defeat it yet again and again find the gem hidden in its body. They decide to take the gem back to the temple and seal it in. After that they move on, making a promise to the mayor of Smallbank to investigate a missing caravan due from Stonedelve.
Arriving in Stonedelve, they learn that their mine has been taken over by formains and this has stopped production. Without further inquiry, they head to the mine to find the formians. While meeting with the guards, trying to speak to their leader, they are attacked by a hidden sniper. The formains attack and combat ensues. They kill the sniper and calm the formains down. They are then taken to the queen. The queen accuses them of being fools. No dwarf has entered this mine in over 500 years. They've been tricked and played. The queen also imparts a dire warning in the form of a prophecy.
Meanwhile the dilettante follows the snipers tracks and finds a bandit camp, who have captured the children of Stonedelve. The heroes return to the village, demanding an explanation. The major tells them that the bandits have taken their children and they were told to get rid of the heroes. The bandits have raided the village of everything and are forcing the dwarfs to make a large quantity of tools. The tools are then shipped north. The heroes leave to village and attack the bandit camp night. They manage to rescue the children, but find no trace of the village wealth. The only clue they do find is a letter...

Unanswered questions:

Why is part of the woods near Treeshine and Stonedelve evil?
What happened to the guardian of the temple of Maitri?
Why did the giant's youths turn into ogres?
What is the mysterious gem and how is it linked to the salamander and the rest of the plot?
Who was the false witness plotting the villages against each other? And for what reason?
Why is it so important that the giants remain hidden?
What was the great war that the giants talked about?
What happened to the dwarven cleric?
Why does everyone in the party dream of the sound of war drums every night?
Why were the bandits near Stonedelve shipping tools north?
Who were they working for?
What is in the letter that the heroes found?
What does the prophecy mean given to the heroes by the formian queen?
What is the obsession that the giants have with gelatinous cubes?

Why are my PC's so content with bypassing any and all plot points? (sigh)