Here's a quick example: https://www.vox.com/2017/6/20/15839626/disparity-between-urb...
Edit: If you give someone a coin with the private key on paper, technically you can give them coin offline, but the rest of the networks have no clue this happened, and you can't spend unconfirmed monies.
Secondly it is only Bitcoin that has huge transaction fees. For example Bitcoin Cash has a next block fee of $0.0015[0].
Thirdly, as noted in the article, 420 million do have internet access.
There are scaling challenges of course, but Bitcoin is not a good example of that. The technical issues come at a much higher usage.
> accumulate hard drive space
The unbanked, like 99% of all others, should use light wallets or SPV wallets so they don't have to store the whole blockchain.
Bitcoin's problems are bitcoin's problems because they are intent on shooting themselves in the foot at every opportunity they can.
Other networks hopefully are run by less hard-headed people that know a bit more about incentives and the importance of liquidity. Dash and BCH are better in this sense.
I call this type of thinking "TED talk ideas" something that looks good on paper with a lot of wishful thinking but fails to consider most of the actual problems
Underbanked people use cash or some financial products targeted at them.
They have more things to worry about than having to worry their bitcoins might disappear because of some shady exchange