Doesn’t the mere act of saying the call to prayer make you a Muslim in the eyes of Islam?
Yup. Part of the call to prayer is the stating have the ‘shahadah.’
The next question is why is it done in such a way from a minaret/tower etc. 5 times a day for all to hear?
Answer: It is not done to only call muslims to prayer and worship, but it is to also remind non-believers about the substance of Islamic belief.
The call to prayer is a form of terrorism to those who do not worship allah.