It's because at the early of 2018 many projects are failed and some of the are scam. This is why investors are losing interest with altcoin and choosing bitcoin for long term investing
the choice in investing depends on the confidence of the investors themselves in choosing long-term or short-term investments and in my opinion there is always a risk that bitcoin investment is a long-term investment with greater risk and requires considerable patience in investing
Bitcoin is investment always risk but we earn good profit for all the time. So experts never say this risk factor because we they know how to survive the any situation. The current situation Bitcoin is the best investment for both short term and long term investment, But day trading is hard to predict but still everyone earn good profit.