The answer is easy, huge returns. You can easily make 50% profit in 1 week without any leverage and over 200% after few weeks/months. There is no way you can achieve the same results in larger stocks.
Small stocks are also easier to trade if you are patient, lack of liquidity gives you many great opportunities as a small player.
The risk is not so high as there is no need to use leverage. And risk/reward ratio is fantastic.
But you will need to be extremely patient and appropriately manage your capital.