How did the term “Sanatana Dharma” became a popular name of Hinduism?

In the scriptures “Sanatana” is used as an adjective rather than a noun to describe a spiritual system. If I call you “good looking” that doesn’t mean it’s your literal name. That’s your quality.

Upon checking by far the most used term for Hinduism by almost all of the great acharyas refer it as “Vaidika Dharma” (Vedic Dharma in English). Arya Dharma may also work because everyone related to Sanskrit and Vedas is call Arya (noble).

So how did “Sanatana Dharma” become the endonym?

You could say “well the vedas are eternal so sanatana (eternal) makes sense” well…thing is “Vaidika Dharma” was already in use. Why fix when it ain’t broke?