The price of Monero has risen less than Ethereum in the past few months, but it has dropped faster. Why is that?
Many don't feel comfortable with command-line so they just keep the funds on the exchange. Having funds so easily accessible, just one click away, makes it a lot more tempting to sell. Multiply that effect with a lot of people and it can explain why there's so many dumps and big price drops as everyone starts impulse selling at the same time, and even buyers are left with XMR on the exchange that they may use to dump price further down in a moment of uncertainty.
Bitcoin on the other hand is easy to store off the exchange which makes it less likely that people will impulse buy. So we have a cycle of slow and steady price increase, and once momentum is gone a violent fast crash.
This is just a theory, and is probably just a part of the reason. Other reasons could include whales dumping to break support levels and acquire more, shorters profiting from falling prices etc.
The liquidity for XMR while still good, is significantly less than ETH so it's easier to drive the price in any direction. Traders will take advantage of that.