i think it's sort of a compounding effect of various societal norms regarding what is considered "masculine and respectable" that causes a lot of friendships amongst men, and amongst cishet men especially, to be very shallow and impersonal.
Based on what I've read, this seems like it's very much a modern thing and that deep male friendship was the norm throughout most of human history.
Relevant poem:
They told me, Heraclitus, they told me you were dead,
They brought me bitter news to hear and bitter tears to shed.
I wept as I remembered how often you and I
Had tired the sun with talking and sent him down the sky.
And now that thou art lying, my dear old Carian guest,
A handful of grey ashes, long, long ago at rest,
Still are thy pleasant voices, thy nightingales, awake;
For Death, he taketh all away, but them he cannot take.
~ Callimachus, Elegy for Heracleitus