Why is the mosque adjacent to the Kashi Vishwanath Temple known as the Gyan Vapi Mosque?

 History is history and we cannot change it. I visited both Temple as well as Mosque and other temples mentioning in my answer.

My view is as follows:

1. Kasi itself has vibrations. Visiting Kasi itself sufficient to worshipping original lingam.
2. South has a tradition of visiting Kasi in one’s lifetime. This will be followed by visiting Rameswaram, another Jyotirlinga.
3. Rameswaram has two lingas. One is constructed by Sita Devi, called Ramanatha Swamy and another brought by Hanuman from Kasi. Though main deity is Ramanatha Swami, you can find Kasi Viswanath adjacent.
4. Another Temple is TenKasi (Kasi of south) for those who cannot visit Kasi on banks of Tamira Bharani in Podigai Hills.
5. South has two lingas from Kasi, one by Hanuman and another at TenKasi.

Both Temples in South are much much bigger than Kasi Viswanath temple in Varanasi.

But remember, it is not lingam, visiting Kasi itself has its own vibrations.