Part of the design philosophy of Piratez is that you dont have a true civilization level industrial/tech base backing you against the invaders. To that end you have 3 general categories of weapons: stuff that you eventually get to buy with the proper contacts, self built, and stuff you can only scavenge for.
Lasers, gauss, and plasma are almost completely in the scavenge category as earth largely lacks the means to build them. Those organizations that can build such weapons are keeping them generally to themselves. You do eventually get to build your own versions of all of these weapons and/or by some earther variants but not in the early game when you might first encounter them.
Edited for clarity and typos, yay tiny phone screen posting.