EM interference with avionics
"Now, tell me: Why (oh, why?) they didn't shield properly this things? Please. Millions of people use airplanes everyday. Each airplane costs hundreds of millions. And they can't protect it from a laptop?"
Aircraft wiring and avionics are by design VERY carefully shielded against known EM threats. The point is that if you have an aircraft (for example) that entered service 10 years ago and was on the drawing board 15 years ago, chances are that the shielding concept is not 100% protecting you against modern day threats, especially those originating from inside the aircraft (like modern mobile phones). As aircraft wiring and connecting hardware make up a significant part of the overall aircraft system weight, shielding concepts need to be designed to provide sufficient protection against (known) EM threats, but not much more than that for obvious (weight and production cost saving) reasons. Finally, in the real world wiring systems (including shielding) degrade (wear & tear, maintenance actions, environmental effects). This may lead to local "leaks" in the EM shielding.
Although all this may not have anything to do with the B777 incident, my advice would be: Switch phones and other electronic devices off when you're told to do so by the crew. There are good reasons for doing so ... trust me.