Why are the conventional methods not suitable for the assessment of biodiversity of bacteria?

Conventional methods cannot be used to assess the biodiversity of bacterial colony due to following reasons:

a) Bacteria cannot be seen with naked eyes hence it is impossible to distinguish them morphologically with naked eyes.

b) Some of the bacteria cannot be cultured in normal media hence it becomes tough to study their morphology and biochemistry.

c) The culture media can easily get contaminated with the other non bacterial organisms also.