I've seen a lot of stories about this in the last year, but I truly wonder how effective they will be. What's to stop people from acquiring equipment like large machinery to dig them out of their bunker or bombing it with bunker busters?

If you look at both past and modern-day equivalents you will see that the rich do buy enough people to work as safety troops.

The reason why Putin or Kim Jong Un is not dead a long time ago is that enough of the ruling upper middle class has been made dependent on their leaders and will work to ensure the safety of said leader.