Usually serving sizes are small, and the people who make it, make a small range of foods, that have been passed down from generations. The food comes from a range of places, lots of Issaan foods, Pattani, rice dishes, noodles. Somtam of course. Sweet, sour, bitter, a full range of tastes that makes Thai food so distinctive. Many foods have origins in other countries but have been adapted by the Thai's to create something new eg Pad Thai
Living in Krungthep (Bangkok) I never went hungry. there is always something open selling food and street food is pretty much everywhere - though there were efforts to limit where it could be sold towards the end of my time there.
Street food perfectly suits Thai eating styles, eating small amounts or grazing often.
I lived in Ramkhamhaeng where there were large numbers of people who had come from the South of Thailand, Pattani district and it was well known for its Pattani style foods. Many of the street food vendors had very low tables and people sat on mats on the ground. My knees struggled with eating like that, old football injuries mean they were not as flexible as once they were.
I did not cook often in Thailand. I could not make the food as well as the street vendors. I grew to have favourite foods, I prefer rice dishes over noodles but I loved to go exploring, walking streets full of people, finding something interesting to try. Ramkhamaeng is not a tourist area, not many westerners there, so people were curious as to what I would eat but they were gracious, told me about the foods, the histories, what to eat with what.