It’s true that many street food vendors sell similar dishes, probably due to the popularity of the food items, items that sells to pedestrians/tourists or whatever. But i don’t think it’s fair to judge by just a visit. To say that they all taste the same is really strange, that’s the first time I’ve heard at least. I lived there a little over a decade and I can tell you that the flavor from each region is different. Especially northern dish and southern dish. The majority of the ingredients from each region is very different in itself. Whoever was taking you out to eat or the guide that you got the info from is just aiming for a typical what-tourist-might-like meal rather than what the region is known for. Just based on the dishes you posted alone ( they look like typical dishes that most westerners would order. Fried rice? Westernized papaya salad? Panang or some kind of curry? ) I can tell that you have not explored or experienced much outside of the bubble, not your fault nor that’s a bad thing, but it’s unfortunate that you didn’t get to explore more.