Ancient Greece was also a sexist culture. “They”, meaning the men, espoused the view that women were intellectually inferior to men. So they specifically celebrated love between two men as the “highest form of love” because it was a true “meeting of the minds”.
Its “sexually liberal culture” was only for women.
And of course, you never read about or encounter depictions of love between two old male philosophers, it was always between an old male philosopher and one of his younger students. So it was also about the abuse of power and perpetuating that cycle.