[fourmii]

Not sure where you're from, but in the US, a fast food meal is far cheaper than buying produce from grocery stores. That is if you can find a nearby grocery store to begin with:

https://en.wikipedia.org/wiki/Food_desert

[nicoburns]

In the UK it tends to work out more or less even price wise. So it's a mostly a convenience vs health thing (ignoring taste preferences).