Because, the first 2 points only can be happen if there’s mistakes on the user side. Not directly to the system or network.
No it is not!
It was explained a few times in this thread what a 51% attack is. This is not "hacking" it's rather exploiting a feature of Bitcoin.
This attack is possible only in theory because in reality you'd need to invest a lot of money before you'd be able to even attempt this and as time goes by it's going to be more and more money. At this point you'd need to rent out a whole nuclear power plant to have enough power to try it. 51% attack is a scary bedtime story for new investors.