With 6% you can't compete with services like coinbase and kraken who charge around 1-2% fees to convert your bitcoin into cash.
Coinbase and kraken never convert to cash. I think those services are not competitors for BTMs.
Bitcoin ATMs are working with cash, which gives more anonymity, requires less effort (go and get bitcoins in 15 sec, compared to sending your docs online and waiting couple of days), in the end you don't need bank account to use bitcoin ATM, however you need one for online exchanges.
I assume BTMs can never operate at the same fees as online services, because they require much more effort to run, not taking into account the initial set up and investment into the machines.