Question

why the injections and drips were put into vein not in arteries even though the veins carry deoxygenated blood?

Answer 1

Usually, arteries are more pulsatile and have more higher pressure than veins. And they are  at a deeper level than veins, which are more superficial and are easily accessible to take blood samples. 
Arteries are accessed only in special circumstances like arterial blood gas .
Hope the answer helped!