Because they are merchants, they travel for a prolonged period of time, and bread will become stale after a day.
If we talk about portability and practicability, something like dried meat, which last long and can be prepared before the journey would be the best bet.
But they also want their food to be delicious, so they need something that gives substance and enjoyable to eat at the same time.
Bread does not typically go bad after a single day. Bread wouldn't have been the foundational food of most civilizations if this was the case.
In fact, many types of travelers bread, biscuits, and crackers could last for months. Add some preserved spreads, meat, or cheese on that and you have a decently tasty meal to keep your strength up.
This should at the very minimum get you to your next stop.
Soup is still easily the worst possible option. I'm sure it's tasty, but does every traveler have 2 or so hours to prepare it for a single meal. Not to mention the days of work it would take to prepare the bouillon.
Wouldn't the fresh veggies easily go bad after a few days?
You don't always have access to suplerflous amounts of clean water or a roaring fire on the go.
And worse, if you dont finish it all, what choice do you have but to toss it? Room temp soup is a great vector for foodbourne illness.
Soup every day is the diet of the merchant that dies on their journey.