I really think that many of those that bought in 2017 were victims of the fear of missing out, they thought the price of bitcoin will keep growing indefinitely and now they are realizing that despite the amazing technology behind bitcoin, bitcoin is like any other asset.
I'm sure most of the people who joined last year have no clue about the technical side of Bitcoin. The price that kept going up continuously was the only motivating factor for them to enter this market.
So yes, fomo has been the main trigger of last year's bull run, which is exactly why it went up that hard, and exactly why it won't be going up this year. Bull runs always happen when no one expects them to happen.
People expecting a bull run this or next year have already bought in, and the newbies who entered last year already have coins and are desperately waiting for the price to recover.
When everyone expects a bull run to happen and have done all the buying in advance, there is no real demand. We have seen what happens when the price breaks through the $7000 mark, we're confronted with sellers only.