If I "steal" a song that you wrote by downloading it, you can still listen to it of course. This is what the pedants love to argue against. The law doesn't call this theft AFAIK, but there are separate laws.

However a producer has lost something - the right to control who listens to it. The right to control how it is listened to, the right to an income from your creation. Various other things that people may or may not agree with but exist in law.

So, to be lazy, non-legal people say they stole the song instead of all this.

This applies to a lot of things such as crypto keys. Knowing the key doesn't remove the key from you. But I have removed control - you can no longer prevent me from taking your tokens/value. It is much like a stranger having a key to your house without your permission. They might never use it. You probably don't want it to be an ongoing situation though.

Can someone steal your password?