The situation with ATMs is pretty much reflecting the actual-demand-on-the-streets... sellers aren't selling and need extra incentives, buyers are willing to buy at much higher premiums.
ATM companies know that they can't really make money on commissions if they don't have bitcoins to sell, and they won't really acquire bitcoins if they can't be tempting enough on their prices that they buy from people. So they need to get those bitcoins, even if at a premium, in order to have something to sell to those who want to buy (and thus make money on the buyer).
We have a situation analogous to precious metals a few years ago when the street market was not correlated with the spot prices - but this is in a greater degree now with BTC.
I think it has most to do with operators trying to keep a balanced inventory. During rallies like last Saturday, bitcoins are at a premium so they raise buy rates and lower sell rates. During panic dumps like the example I posted from last August, the operators have an excess of coins relative to their fiat supply, so they lower buy fees and raise sell fees. It also means that panickers and FOMOers pay a premium for their foolishness while cool holders get a bargain.
The 2 examples I gave are extremes but if you play it right, the ATMs are cheaper than transferring fiat to and from exchanges and paying the exchange fee. Of course this only works if you're buying dips and selling peaks.
The big advantages of using ATMs though are security, anonymity and instant gratification.