Fake news was an own goal by the left wing press. After selling a fable to their readers about a Clinton landslide, they tried to deflect by blaming the election outcome on fabricated stories. But there was never any evidence these stories had more reach and influence than what mainstream outlets were peddling. Same way there is no evidence Russian Facebook ads and social media postings eclipsed the millions e.g. the Clinton campaign spent to Correct The Record. Similarly, laments about r/the_donald were categorically ignoring how the default news and politics reddits had become unofficial Clinton cheering squads with moderators complicit.
Most ironically, lefties lamented the ignorance of right wing voters in accepting stories that confirmed their bias and preconceptions, while they themselves eagerly accepted the fake news narrative.
Fake news was not an important concept. Media manipulation however was, and the two got conflated for very obvious reasons.