Recently I began a new play-through of my werewolf Dragonborn using a mod that allows me to become a werewolf when the moon is at a certain stage or full etc. I know that in Morrowind's expansion 'Bloodmoon' there were lunar transformation, but is there any particular reason as to why it is the moon(s) that make a person transform? to my knowledge Hircine doesn't have any relation to Masser or Secunda..

So I ask, why is it that people transform into werewolves because of the moon?

In Bloodmoon you transform every night, no exceptions.

The death of Lorkhan at Boethiah's hand signifies the triumph of a Daedric Prince over Lorkhan. The full presence of the divine corpse in the night sky acts as a beacon to those who would hunt, as it is a symbol of Boethiah's successful hunt on the creator of the mortal plane. It is thusly reflected in the creation of a Daedra Prince (werewolves) in triumph over the creation of Lorkhan (mortals) in full view of Lorkhan, as the werewolves try to emulate the original hunt to make their master proud.

/fanwank (I'm not very good at this)

There's no official reasoning given, as far as I know.