Now we see that Bitcoin is going wild again. Why did Bitcoin fall the first time, from $20,000 at the end of 2017, to $3,500 by the end of 2018?
Basically because of miner's fees.
wrong.
price started falling from $20k because $20k was a bubble. it reached $3100 as the bottom because near the end the whale manipulation was at its peak. it had nothing to do with transaction fees.
this is not the first time we see a roller coaster action from bitcoin. the $20k bubble was repeated at least 4 other times before in the same exact manner!
Transacting in Bitcoin wasn't profitable, because miners got together and raised their fees so high that it wasn't worth trading Bitcoin.
i seems like you think bitcoin is a centralized bank with miners as its owners!
the reality is that miners are only workers that we have employed to do the "job" of finding blocks. the fees went up because of the fee war due to number of transactions wanting to be in blocks surpassing the size of the blocks.
the only thing you can blame miners for is whether or not they were participating in the spam attacks of 2017 and whether they were one of the many groups that deliberately spammed bitcoin to increase the backlog and start the fee war that increased the fee. but that would be a speculation and an entirely different discussion.