Because over the years, Bitcoin has performed strongly with significant returns and continuing. Bitcoin yielded greater returns than any for 5 out of the previous 6 years (2011- Bitcoin +1500 percent, 2012- Bitcoin +299 percent, 2013- Bitcoin +5400 percent, 2014- USD +13 percent, 2015- Bitcoin +37 percent, 2016- Bitcoin +130 percent).
When compared directly against Bitcoin, however, Amazons returns only outperform the digital currency in 1 out of 4 years. Christmas timed investments of $1000 yield Bitcoins returns outperforming Amazon significantly if entered in each year except 2013.