the reason is, the world is in different stages of infection......

the reason is, the world is in different stages of infection... what is relevant in Italy with huge numbers of people infected and many already with immunity is not same as Australia where we have
been able to somewhat flatten the curve and there are only 6000 infected patients... not much herd immunity.
so the use of this test can’t be applied equally to different countries with different patient infected numbers.

thats why it’s important to understand who this test will target - is it for diagnosing new cases ( countries like Australia with small numbers and no herd immunity) or for diagnosing people with immunity who had cleared this infection and have established antibodies ( which is more Italy, Spain, Germany, USA)

and antibody test is good for detecting immunity not new infections

hope this answers your question