Why does the rickettsia test exist if it isn't accurate or accepted?

Complicated answer: Even when tests are highly sensitive and specific, how well they can tell a patient if they have the disease or not (positive and negative predictive value) is highly dependent upon the prevalence of the disease. Tests such as this are useful only if the clinical situation supports the diagnosis (we call this pre-test probability).

Depends on the test.: If the test is one of the old weil-felix tests for rickettsial disease which rely on cross-reacting antibody between certain strains of the bacterium proteus and certain rickettsia, they are worthless in today's world. The more modern antibody tests for rickettsia are better, more sensitive if done properly but still some crossreactivity with other rickettsiae.