ya it seems that the income of these cart vendors goes up and down quite a lot depending on the season/holiday/weather.
Some seem to make a lot especially in cities like New York but the also work hard. Personally I prefer working inside an actual building. In the video she stands outside all day in the hot sun burning her skin, not to mention where to takes washroom breaks.
I worked at fast food before and it was quite easy and fun at times compared to working outside by yourself.