Of course it is true that no-one can open your door, but it is not true that the house cannot be robbed. The thief can smash the window, pick your pocket when you are on the street, trick his way into your house and so on and so on.
A better analogy would be that you have a house made of the strongest materials known to mankind. It's entirely impossible for a criminal to break into the house without creating new, vastly better weapons which do not yet exist and expending enourmous amounts of resources in the process.
However, if the person living in the house decides to throw their money outside of the house (spending it) or give it to someone else to hold it (an exchange) or they open up a big hole in their house that lets someone walk through, their funds can be stolen.
Notably, if you have a bank or PayPal, someone can install a keylogger on your computer and take your funds if you input your details.
Similarly, if you expose your BTC private keys (or seed) to the Internet in any way, there's no guarantee that your funds are safe. But
with Bitcoin you can store your money on a piece of paper or an airgapped computer which is never connected to the Internet at all. Can your bank do that?