Its not a good thing to store your BTC in these exchanges regardless of how much interest they are going to give. Its just not worth it
For you and me it's not worth it, but there are enough people that aren't looking at things from our point of view. If you browse through the forum, then the far majority of the lower ranked members are constantly looking for ways to increase the number of coins that they have. One person tries it through cloud mining, the other tries it through ponzi and hyip schemes, and others just go for services offering interest over their coins. They discard all possible risks because their greed is blinding them.