Actually, more and more website and stores are accepting bitcoin payments (see link) https://99bitcoins.com/who-accepts-bitcoins-payment-companies-stores-take-bitcoins/. When crypto currency first made an appearance with bitcoin, it was mainly used on the dark web as a currency due to the difficulty in tracing back the buyer and seller.
Furthermore, you are viewing crypto currency simply through the lens of bitcoin when many such currencies exists. As with stocks, to mitigate such risk you must diversify your portfolio to ensure that if one currency drops the other currency will thrive (example: invest in Bitcoin, Ethereum, Ripple). With the recent drop of bitcoin, ripple had managed to stay a float (see second link posted https://xrpcharts.ripple.com/#/markets/XRP/USD:rhub8VRN55s94qWKDv6jmDy1pUykJzF3wq?interval=1d&range=6m&type=candlestick (one year or max view, candlestick chart).
As with any investment, it's value can drop and be worth nothing (see Enron Scandal). Any risk averse individual should not get into crypto currencies.
Holding the currency for a couple of years is actually considered a long term strategy. I do agree with you that some of the crypto's are short term trade strategies based on their volatility, but others with enough research can be held in the long run depending on what they are used for.