Sysco is a food DISTRIBUTOR. They bring food products to a retail establishment or restaurant or institution based on what the OPERATOR orders. And they generally do it at a pretty competitive price.
I have worked in places where everything was made from scratch (and purchased from Sysco). Likewise, some places rely on pre-made items.
I have attended a number of distributor shows over the years - Sysco, Gordon's Food Service and some regional players. Items that are generally made not bought: soups (look for names like lumberjack vegetable, etc.) desserts, salad dressings, prebreaded fried items. chicken kiev/cordon bleu, etc. It is all pretty easy to identify.
Any smart operator prefers to make the items from scratch as it it tends to be a lot cheaper in the long run to produce your own products.
Also, like MOST distributors, they offer "good, better, best." In other words, they can offer a real low price to those in the industry at the low end food operations. (Let's be blunt, some places like nursing homes have a budget of about $3 per day for food cost.) They also offer top lime products that could be served anywhere.