The system relied on ability to same the population accurately, and on the almost one-to-one relationship of phones to households. The introduction of cell phones undermined that.
Also, in the past the mass media were politically neutral, but now almost none of them are. People tend to tell pollsters the “right answer” based on what the pollster is perceived as expecting to hear, so if the media trend to be left-wing, the polling results tend to favor left-wing candidates and positions. This has shown to be a factor in many countries, including Israel and Britain.