The huge price pump back in 2017 was made from F.O.M.O ,
And most of the investor's was just getting in and doesn't really know anything about crypto,
Most of them just bought it because of recommendation and thought that it is a quick way to be rich.
So when the market starts to crash down most of those investors have F.U.D and sold their crypto.
it wasn't exactly like that.
most of the price rise in 2017 was because of two major positive news. first one was the mass adoption of bitcoin by a couple of countries such as Japan as a currency and second was the end of the scaling debate that was keeping bitcoin back for over 4 years.
of course FOMO was a part of the market like it always is but it wasn't the main reason, not even the biggest one. and it mainly happened near the end which was also because of being in uncharted waters of $10k+ range that the rise happened smooth and fast.
same with the drop, it wasn't all because of "FUD". mainly it was the bubble burst, specially the early stages and near the end the FUD was the dominant factor pushing the price below the realistic values.
ps. don't confuse what happened to bitcoin with all the "cryptos" the altcoins were mainly pump and dumps and still are.