The basic problem is that if you grew up in the U.S., no matter how healthy your are, you haven’t developed defenses against all exotic bacteria. And the stress of travel, the different schedules and missed routines can decrease your immune system so that you’re ripe to pick up bacteria from something as innocent-looking as a stalk of celery. Even a cold, uncooked soup like gazpacho can mean trouble. And because it’s impossible to know what the animal you intend to eat was eating before it got to you, odd species like snake and rats are not to be trifled with.
The next problem is how the food was handled, even in the finest restaurants. Hell, 67 out of 78 people dining at Noma in Copenhagen, considered by some the best restaurant in the world, got food poisoning in one night. But the odds stacked against really mount in street foods, when running water is rarely available.
This is an excellent article on Food Safety when traveling, and on food safety in general.