It is not called the major fifth because the interval distance and characteristics between them are different from the major fifth.

In music theory, a perfect fifth is the distance between two intervals of seven semitones. It is called the perfect fifth because the frequency ratio between the two notes in this interval is close to 3:5. This is a pure interval and has harmonious properties.

At the same time, in music theory, there is another interval called the major fifth. The major fifth refers to the distance between two intervals of four semitones. For example, there is a major fifth between C and G. The difference between a major fifth and a perfect fifth is the distance between them, with the major fifth being three semitones less than the perfect fifth.