Think of ordinary tomatoes for example. In its raw form a tomato goes bad after a few weeks (depending on how it's stored), as a store you got to discard a bunch of them before that time because the tomato develops blemishes from handling/storage, and the tomatoes have to be handled more sensitively and with more effort.
Now, take that tomato and can it straight after harvest, together with a bunch of preservatives. It now has a far longer expiration time in the order of years, it doesn't need cooling, and tomatoes that come from the field with blemishes can now be used as well, just cut them up, remove the unsightly pieces and sell it as cut-up canned tomatoes.
From here on, the calculation is the same for both kitchens and low income populations... both need tomatoes to cook a meal. So what do they prefer? Fresh tomatoes where one now also needs to take care of leftover tomatoes and do another meal before they expire, or canned tomatoes that are cheaper to source and easier to match with actual demand?