I have read on somewhere that:
"Do not run Metasploitable (an Intended Vulnerable Virtual Machine) in your Bridge Network."
Why? Does it create a bridge to the attacker's system directly? If yes, how does this happen?
If you run Metasploitable bridged in your network, the VM is connected to the network directly. Everyone in the network has access to the VM so everyone can exploit the vulnerabilities.
The VM runs on your host so an attacker can use your resources. It could also be, that the attacker could escape the VM and attack your host device.
You should use a host only adapter to prevent this.