Why bitcoin is pseudonymous and not anonymous?
Bitcoin is pseudonymous. Sending and receiving bitcoins is like writing under a pseudonym.
If an author pseudonym is ever linked to their identity, everything they ever wrote under the pseudonym will now be linked to them.
In Bitcoin Pseudonym is the address to which you receive Bitcoin. Every transaction involving that address is stored forever in the blockchain. If your addresses ever relate to your identity, every transaction will be linked to you.
Bitcoin is not anonymous. Bitcoin is often described as an anonymous currency because it is possible to send and receive bitcoins without giving any personal identifying information.
Achieving reasonable anonymity with Bitcoin can be quite complicated and perfect anonymity may be impossible.