I get that until recently it was considered normal and relatively cheap, but you are literally paying someone else to make food for you.
It can’t be sustainable without exploitation of workers and/or animal welfare to have that available to the majority of people on a regular basis.
If you can only afford fast food as a luxury, to me that seems like a good thing.
Even though the reasons for buying these products are different, the mechanics are surprisingly similar.
Here’s an example. A nicotine addict has to choose between keeping on smoking or going through the struggles of quitting. Someone driving a car has the choice of keeping the current job, or going through the trouble of finding a job that happens to be within cycling distance. People tend to pick the easier option, even though there are good reasons for going through all the trouble.