Monero, unlike Bitcoin, does not use a transparent blockchain but rather an opaque one, using a method called as ring signatures.
These ring signatures are essential in making Monero completely private and anonymous. It achieves this by means of redundant transactions.
For example, A has to transfer a certain amount to D. While in normal bitcoin transaction this would just include reduction of wallet balance of A and addition of wallet balance of D, this is not the case in Monero. Dummy transactions of different sizes are sent from A to B and C, who then in turn transfer the same to D.
Thus in a large enough exchange network the number of such redundant transactions would be so high that effectively identifying the sender and the receiver would be impossible. This is reminiscent of traditional banking where transferring money does not make your other transactions, or total balance a public knowledge.