【Learn Chinese】Why are there so many languages in China?

This is a very good question, and again, the answer is extensive.
To keep it short, China has a very long history of thousands of years (3,500 of written history to be precise) and its territory didn’t always look like the one you know today.

Kingdoms were unified and territories expanded, with large groups of people bringing in their own languages, traditions and foods, creating this rich linguistic culture we know today.
Over time, many languages in China went extinct and despite the strong promotion of Standard Chinese as the national language after 1912, many languages and dialects kept their identity and are still very well preserved today.
One of the reasons for this linguistic preservation is geographical. Indeed, many refugees settled in remote and isolated areas for safety, and did not have much contact with the neighbouring regions.
Their languages didn’t receive any, or very little, influence from the outside groups, and thus couldn’t evolve like many others did.
Some groups can understand each other (mutually intelligible languages) whilst others can’t (mutually unintelligible languages).
The word “group” might make you think of a small number of people but keep in mind we are talking about millions of people!