First, let's clarify the difference between accounts and addresses.
"Accounts" are used to help people track their funds. This is mainly used to track the source of funds. Since this is just tracking, you can move Bitcoins from one account to another by moving a number from one column to another. No transaction is necessary. (It's like if you know you owe $ 25 to your son for an allowance and you have a $ 200 budget for groceries.)
"Addresses" are used to receive Bitcoins during transactions. The coins are sent to an address. The customer associates each address with an account and adds the funds received to that account. This is simply done for convenience to allow people to know indirectly how the funds were sent. But you can have any number of addresses associated with the same account.
The change comes from the way Bitcoins are spent. To spend a certain number of Bitcoins, you must extract Bitcoins from the transaction outputs to the accounts you control. Note that in the expense part, no matter the address or the associated account. When you spend Bitcoins from a particular account, it simply means that you debited this account the amount you sent. This does not mean that funds come from addresses associated with this account. Remember, the association between addresses and accounts is for to receive only, not sending. (For example, when you spend money in the grocery store, it's not like you have specific bills for the grocery store.You just have a budgeted amount.)
Thus, when you extract transaction output, you form a stack of Bitcoins large enough for the number you are trying to send. Generally, this will not be accurate because you must claim an entire exit. So, the excess forms the "change".
Since there is no address associated with sending Bitcoins, there is no particular address to which the change should be sent. Thus, to preserve the anonymity, the customer creates another just to receive the modifications of this transaction. Since this address is not really associated with an account and should not be used to receive more Bitcoins (because it would insensibly tell people that the same recipient received the coins as he had this change), the client does not display it.
Since the customer manages the parts in a particular way, it makes no sense to see the parts he manages with any explorer. It is precisely to try to hide the fact that all the pieces are related. These types of services are intended to monitor received funds, unmanaged funds.