Unspent Transaction Outputs (UTXO)
Bitcoin originated a trasaction system called UTXO or Unspent Transaction Outputs, which reroutes unspent funds from a transaction into a new public address for you. This is because each public address has a private key derived from your seed that must be used to create a transaction. However, the way in which this private spend key is used, makes it easy for a computer to figure it out if used in several transactions. Therefore after sending one transaction from a certain public address, that address is considered unsafe for future use and a new one must be used to receive future funds.
Example: You have 10 BTC and want to send 1 BTC to your friend. Your wallet application uses your seed to find a new public address and its private spend key. Then creates the transaction sending 1 BTC to your friend and 9 BTC to your new public address. Now, if you friend wants to send you BTC back, you must provide them your new public address.
Other cryptocurrencies use reusable accounts that make it simple to store a contact and send funds without having to change public addresses all the time. This makes it as simple to share public addresses as a phone number or email address.