I'd say it's because politics has become a more self sustaining machine, independant of the people.
In my opinion people didn't vote for Donald Trump. The voted against Hillary Clinton and the political machine she represented. Just as people didn't vote for Tony Abbott in 2013. They voted to get rid of Kevin Rudd. Politicans are doing their own thing more than ever. It is only when a group has enough power, mostly through social media these days, that they will listen.
Voters are left with not a lot of choice. Gone are the days where you could vote for a party that mostly aligned with your beliefs. Now it's voting for the one you dislike the least.
This phenomena has been repeated around the world. E.g. Look at the recent Ukranian election.
