I just remembered the poly network heist, one of the biggest heist in the history.
Is there also a possibility BTC can be hacked?
If it is, I bet every currency will start to declined.
How safety BTC security for you?
Want to know veterans answers.

Why are you compare the Poly network with bitcoin ? Look at the market cap and price of both the coins and you will know why people invest in bitcoin. The reason is that bitcoin blockchain is designed in a way that there is almost zero chances that it can be exploited. On the other hand, Smart contracts like Poly etc can easily be hacked if thee is any bug left by the developers.