Questions regarding hardfork bitcoin

[kemalramdanu]

Before I apologized if someone had discussed this before Smiley
Since I knew bitcoin, I experienced several times there was hardfork on bitcoin.
As hardfork on bitcoin last year became BCD and BCH.
When bitcoin happens hardfork, the BTC holder suddenly gets BCD or BCH (at that time), even though the number is not much, but it's worth and is shared across all BTC holders on the entire blockchain network.

What is my question, which BCD and BCH are sent from?
If that is indeed the BTC fork fraction that we have, isn't the amount of our BTC not reduced, but the reality is not so.

Maybe someone here can explain, thank you.