Lack of facilities especially in third world countries.
Serology:- patient with defect in their immune system produce very little antibodies , making it the technician to detect the antigens instead.
Fungi are not present in blood, they are localized in the tissues. These require tissue biopsy or precipitins test. The other problem with Fungi is that, they are common lab contaminants, hence a technician is forced to do repeatedly culture before confirming the results.
In virology, culture and serology takes between 1-4 weeks depending with test. These a long period for any given patient. This affects hospitals that have no resources to invest in modern equipments like DNA hybridization technology.