I so do not get this
Include me as one of those experts.
To put things in an idiotshell (nutshell does not do it justice): The pilots overflew their destination by 150 miles, which means they went about 250 miles, or 30 minutes beyond their descent point.
They went 400 miles, or about 50 minutes, without talking to anyone. Getting lost on the frequency handoff between sectors happens occasionally, either through a controller directing the crew the next frequency and not noticing the absence of a readback because the crew missed the call, or the controller forgetting to make the hand-off in the first place.
It happens. No big deal. There are several means to overcome this: controllers attempting contact through other aircraft in the area, transmitting on "Guard" (while airborne, radio 2 is set to a common monitoring frequency), or telling the companies operations control to send the new frequency to the crew via datalink.
No big deal unless all efforts are to no avail, over a prolonged period, as here. That raises serious issues about crew situational awareness.
Not to not worry, they get even more serious.
At Northwest/Delta, flights over one hour require recording fuel and arrival time at least once per hour. Clearly, they weren't doing this.
But wait, there's more. The ancient, hand-tooled, traditional round-dial approach to flying required deriving information from a fair amount of abstract data.
The aircraft with the headless vectors (all speed and no direction) at the controls was an A320, this picture is from an MD11. However, for the point at hand, the distinction is without difference. The crew had to completely ignore, or be droolingly ignorant of, certain very graphic symbology.
To wit: in the center display, the line down the center represents where the airplane is going. It is never not there. Well, okay, sometimes in flight re-programming of the Nav System can lead to the magenta line disappearing. This is always accompanied by "holy cr*p", and immediate action to unscrew the thing. It is never not there, but it will not be there after overflying the destination.
Here's my best, expert guess. The crew took off their headsets on reaching cruise altitude. Absolutely standard procedure. Unfortunately, both pilots forgot to turn on their overhead speakers. This rendered attempts to contact them by radio mute.
However, it also requires them to utterly deaf to the fact that silence on the radios is not normal. (Unless one is transiting the depths of Canada even further into the night, that is.)
And not pay attention to the flight plan.
Or the airplane.
Or the clock.
Or, well, you get the point.
Nearly all aircraft mishaps have a fairly lengthy chain of circumstances for them to occur.
Not this one. All it took was two guys with room temperature IQs and a perfect lack of professionalism.