There are a lot of reason and the thing you mentioned just a single one. Price of the whole cryptomarket dumped and pumped everyday, it's really normal cause if you are a trader you can see it happen several times in a day cause it's the main way trader earn money ). They buy in low then sell in high. If the price always stable or increase all the time I think nobody will join trading anymore cause there are no ways to earn money in trading if this case will happen.