If that's the case, a luxury of convenience, then fast food was and still is a luxury. Or maybe fast food was an $affordable luxury of convenience and now it is an $$$expensive luxury of convenience. Ok, that makes sense to me.
I dont eat much meat, but i still like a good crispy chicken sandwich- now that costs $12, is so brined and salty i get kinda grossed out, and has 3 gristley bits i have to spit into a napkin. And i sweat grease and stink for a day.
A luxury is something extravagant, high quality, and highly enjoyable.
30 years ago, fast food may hit the "highly enjoyable" part... but now, for many, it's hitting the "something extravagant" part because of the cost (proportional to their disposable income)