Bhagavad Gita, Chapter 4, Verse 3

I have this day told you that same ancient Yoga, for you are My devotee, and My friend, and this secret is profound indeed.

This isn't being handed to just anyone, it's being given to someone genuinely ready to actually receive it.

Krishna names exactly why Arjuna, specifically, is getting this teaching: not rank or achievement, but real trust and openness. Some things only land when the person hearing them is actually prepared to take them in.