Where I'm from, tax laws are not that effective also. And for a number of reasons. For one, there are many ways to be dishonest with your income and you will pay only a small amount or none at all. Or you don't declare anything at all and shirk tax responsibilities altogether. Or somebody will do the trimming of taxes for you. Or you're a rich and powerful person that even government authorities won't bother you about taxes. I'm not even saying all these are illegal. After all, tax avoidance is legal.
Indeed, those who are formally employed are the ones who cannot evade because taxes are automatically deducted from their salaries.
Maybe your country is still among those countries who are slow to improved. If we think we are earning enough then we must willingly pay our taxes to the government so that we will have a peace of mind and it does makes you feel good knowing that you are helping your country to recover or grow.