And, how, do these disenfranchised / persecuted people turn their not-in-the-bank money into WhateverCoin ?

By giving cash to a shady backstreet exchange guy? Or maybe using a payment kiosk to top up a mobile phone / whatever other service the P2P seller can get the money out of.

But more likely scenario is they have friends who let them use their bank accounts (but don’t have friends who let them use their good overseas bank accounts, so not that useful).