Why was the guitar used in so many cultures?

While the guitar is indeed a popular instrument with a wide cultural reach, it is not as universal as your question implies. While guitars are commonly associated with cultures that derived influence from European traditions, many cultures have their own string instruments that serve similar purposes.

It's important to recognize the diversity of instruments across different regions and cultural backgrounds. Instruments like the kora in West Africa, the sitar in India, the guqin in China, and the charango in South America are just a few examples of string instruments that hold significant importance in their respective cultures.

While there are similarities in the functions of string instruments, such as producing melodic and rhythmic sounds, their designs, playing techniques, and cultural contexts can vary greatly. Understanding and appreciating these differences is essential for comprehending the rich tapestry of musical expression across the world.