why is this loop only running once and not finishing the rest of the script?

Your module script will never get to the return line so the could will block at the while loop.

Example:-

-- script
print('start')
print(require(script.ModuleScript))
print('done')

-- module
while wait(1) do
	print('a')
end

return true -- cannot get to the return

You can use spawn to create a new thread around your while loop.

Example:-

local dropper = script.Parent
local loopWaitTime = dropper:WaitForChild("LoopWaitTime")
local oreValue = dropper:WaitForChild("OreValue")
local dropperPart = dropper:WaitForChild("DropperPart")

-- run codeas thread
spawn(function()

-- you need to think about how you will stop the loop
    while wait(loopWaitTime.Value) do 

        local newOre = Instance.new("Part")

        newOre.Name = "Ore"
        newOre.Parent = dropper
        newOre.Size = dropperPart.Size
        newOre.Position = dropperPart.Position

        game.Debris:AddItem(newOre, 25)

        local cash = Instance.new("NumberValue")

        cash.Name = "Cash"
        cash.Parent = newOre
        cash.Value = oreValue.Value

    end
end)

return true

I hope this helps.