I'd like to think it was a combination of all the online shopping sites for all your non-groceries that started killing them off.
Why go to a mall to buy that hat you always wanted when it's not only available online on the website of wherever you are planning to go but could be cheaper? That, or just buy it on Am*zon.
That, and I firmly believe people in various first world countries have gotten lazy enough that they'll gladly wait the however long it takes for something to arrive by mail, but spending the time to have to drive somewhere and walk from the parking lot to wherever in the mall the store they want is? Haell Nah! Combine that with inflation (meaning higher gas prices) and you have people not going to malls unless they have to.
It's why surviving US malls usually have something to keep them alive to attract people anymore, I swear. Some sort of gimmick like that one well known mall with the amusement park in it or how the mall near where I live has an aquarium in it (never been, so I don't know how effective it is at attracting people). I don't think the restaurants you'll find in malls are even enough to attract enough people keep malls afloat, either, but I could be dead wrong about that one.