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.
Everybody pays tax, or better put, everybody should pay tax, it doesn't matter if you're poor or rich, as far as you earn an income and have assets you should pay tax. Tax is just usually higher for higher income earner in most countries.
The problem is government officials and politicians are too greedy enriching themselves than building better places for it's citizens, especially in developing countries where there is no proper system. So if you live in that type of country you have to realize that you're in your own. People in developed countries with a working system don't have it easy but it's worse in a place without a system.
As much as countries are filled with corrupt systems, you still have to obey the laws or you'll be punished, so you have to pay your taxes.
Of a truth every one is required to pay taxes to government if only the system was to be transparent such that the dividends of the taxes the masses are paying are visible to them but however, except a poor man has a source of income they should not be taxed. The poor ones in the society are trying to survive so they don't deserve pressure to pay taxes because had it been the so called government were to make good use of the revenue being generated by people who pays their taxes it would have had significant results in reducing the rate of unemployed youths on the streets but it is just so sad that after collecting this taxes, they don't care to bring forth projects that will employ higher numbers manpower to deliver them by so doing everyone will even persuade others to pay taxes and people would gladly pay without delay.
Instead of the government to use this income that is generated for infrastructural development and other projects, they often share the money among the themselves and enrich their businesses while the masses are there suffering yet they are still paying taxes.