In one word the reason is volume.
From peak to peak the trend is still mostly down over a long term, like month to month. The only uptrend that has formed is extremely new and short term, days to a few weeks. and furthermore the volume of trades is extremely low, giving very little strength to this rally. From a technical analysis point this is not a sustainable rally.
Also, fundamentally cryptocurrencies are beginning to experience regulation from most governments, at this point they have gotten too big for governments to ignore. This also will lead to a period of volatility and most likely lower prices for cryptocurrencies till a balance is reached between regulations and cryptocurrency use. Once that balance is found prices will then most likely rise and will rise with volume confirming a trend reversal to a new upwards trend.
A possible reason why we are seeing a small rally that isn't sustainable
The Olympics began close to the same time as this rally. The Olympics are located in Korea this year. Korea has became the hottest spot for cryptocurrencies as of lately. A rise in tourism sales and just all around money transfers is bound to have happened as a result. Not to mention we have seen rallies before as a result of people talking to each other that like cryptocurrency and exposing others that haven't heard of it or bought it yet. With Korea being the biggest hotspot for cryptocurrency and a large amount of tourist coming that may not be involved in cryptocurrency yet, we may be seeing a similar rally like we saw during this last years holiday season.
Of course though the Olympics will end soon and at that point the overall trend will resume if the Olympics is the major reason why there has been a rally recently, that that overall downtrend will come back, if there is something else that is causing the upwards rally then prices may continue up and this might actually be something more sustainable than a shortly lived uptick in the longer view of things.
Also, did want to make a shoutout to Steem which as remained stable still at $5 USD through out the last few months both as Bitcoin prices fell, and rose recently. Which in my book adds to Steem being the best true cryptocurrency that actually has the characteristics of a currency. Namely a stable value and means of transfer.