Here's why:

* Normal flora refers to the microorganisms that live in or on a healthy human body, typically without causing harm. This term is older and sometimes considered less precise.

* Microbiota is a more modern and comprehensive term that encompasses the entire community of microorganisms (including bacteria, fungi, viruses, and archaea) found in a particular environment, like the human body.

Both terms essentially refer to the same concept, but "microbiota" is now the preferred term in scientific literature.