They weren’t always there, but they certainly wound up there as his Presidency dragged on and things like Obamacare began to hit people’s wallets. Where it wound up is what matters, as people can’t disapprove of things that haven’t happened yet (except in Trump’s case, where some Democrats were calling for impeachment before he was inaugurated).

Yes, mass protests tend to be a symptom of widespread and strong opposition

The protests were driven by the media’s response, which were unlike anything that any candidate has faced before. The media was furious that they were unable to influence the election for Hillary, and then they realized that they could profit from the polarization. With enough negative media coverage, anything can sound like a big problem to those that allow the media to shape their opinions.