Honestly, for the people I know just about every reason they go out to eat can be brought back to convenience.
Learning to cook well is a significant investment of time, and avoiding that by going to restaurants (apparently there are some people who do this almost every night?) where they have people that have already learned to make high-quality food (whatever "high quality means to the person - McDonald’s, believe it or not, is a high-quality example of what it’s intended to be) is convenient.
Having a large gathering at a restaurant multiplies that effort, avoids setup, cleanup, and the other hassles associated with large gatherings. Again, convenience.
Cooking multiple dishes so everybody in a small-ish group can have what they want (as opposed to sharing a communal dish) is hugely inconvenient (but not necessarily completely impossible) in a residential kitchen.
You could argue that most of those things slot into other parts of that diagram as well, and that ordering from a restaurant is actually a basket of separate-but-related purchases (a grocery shopping service, a preparation service, a cleanup service, etc.). And you’d be correct.
But for just about everybody I know, if you do the “five whys” about why they eat at restaurants you’ll hear “convenience” sooner rather than later.
As for those squares, the idea of those meal replacement squares being convenient is true - but it misses the obvious point that there’s a minimum quality threshold that has to be met before convenience enters the picture. It’s a pretty low threshold for most people, but it’s absolutely there. It’s one of the reasons why we don’t just carry around baggies of gourmet dog kibble in case we get hungry. Most of the high-end kibble is prepped to higher standards than human food, and it would be hugely convenient. But it fails that quality threshold, perception-wise.