So, why don't they tax the poor who barely struggle to eat?:Simply because they found those set of citizens useless and the prison will be occupied if charge them for not paying taxes since there are more Poor people than the rich in the society.
We all get taxed whether you are poor or rich; if you are poor and you have a small parcel of land, you are not exempt from the tax; they will tax you; taxes are uniform. They don't care about their status in society, but you still get taxes; you buy food, and the food you buy has taxes; there are some services that the government taxes, whether the poor or the rich use it.
We cannot escape taxes, especially if you're living in a third-world country where the government keeps looking for ways to tax its people, whether they are rich or poor.