For cryptocurrencies to be commonly used by the general public they must gain trust. The same trust that people have in the bank coins and notes they use to buy goods and services.
exchanges are used by traders not by the "general public" so why should they even care about the security of these exchanges?
also what does this have anything to do with "security of c ryptocurrencies" which you put into your title here?!!! it seems like nobody else read the comment itself and mainly are focusing on the title! a cryptocurrency is only safe as long as its code is safe and its network is safe from attacks and a couple of other things. but its safely has nothing to do with the safety of the third party services that are using it.