The use of 6.4mm audio jacks in the audio field is primarily attributed to several reasons:

1. Audio Quality Demands: The 6.4mm jack, compared to the smaller 3.5mm version, offers a larger physical size, which contributes to better audio quality. Audio quality is a fundamental requirement in audio applications, especially in professional music studios, live performances, etc. The larger size of the 6.4mm jack helps reduce distortion and provides a richer sound experience.

2. High Power Output: Certain audio devices require higher power output, such as audio amplifiers and instrument amplifiers. Due to its larger contact area, the 6.4mm jack can handle high-power audio signals more effectively, while minimizing potential heat loss and distortion.

3. Professional Applications: In settings like music studios, recording studios, and audio shows, the 6.4mm jack is often the preferred choice due to the higher demands for sound quality and signal stability. Professional audio equipment commonly supports multi-channel input and output, and the design of the 6.4mm jack facilitates meeting these requirements.

4. Compatibility: In the past, the 6.4mm jack was one of the most common audio connectivity standards in audio equipment. As a result, many legacy audio devices and instruments still utilize this jack. This compatibility factor maintains the widespread use of the 6.4mm jack in certain scenarios.

However, it's worth noting that with technological advancements, some modern audio devices might also adopt other jack standards such as 3.5mm, XLR, RCA, etc., each offering its own advantages in different application contexts. Hence, the choice of jack often depends on specific requirements, device characteristics, and usage scenarios.