Why is contact necessary for charge transfer?

Question

I’m familiar with the idea of polarity and I know you can induce separation of charges within an object. But why can’t actual transfer from surface to surface (i.e. triboelectric effect) occur without actual contact?

Answer 1

There is probably some charge transfer without contact because the air in the “gap” can become a conductor if the local electric field is strong enough.
After all, when there is a spark from the dome of a Van de Graaff generator to an earthed conductor there is a transfer of charge without the dome and the conductor actually physically touching.