Why is the plug on e-liquid vials so big?

The plugs we use for our vials in recycled PET are all equipped with a dropper to guarantee the proper dosage of e-liquid. They are also equipped with a tamper-proof ring and child-proof safety cap (ISO 83 17) which must be of large size to (ISO 83 17) avoid opening too easily. The plugs we use for the American market are in compliance with American GCC legislation.