There are multiple crypto-currencies data sources, but a small proportion of them give a convenient way of extracting crypto-currencies data automatically. I found the easiest to work with to be https://finance.yahoo.com/cryptocurrencies, [YF1].
(I also looked into using https://data.bitcoinity.org and https://www.coindesk.com/coindesk20. )
Remark: The ...
It doesn't work because of this:
getReturns[lst_] := (lst[[# + 1]]/lst[[#]]) - 1 & /@ Range[Length[lst] - 1];
FinancialData returns a TimeSeries. The Range[Length[lst] - 1] goes from $0$ to $n-1$ so the zeroth element, which is the head TimeSeries ends up in the calculation of the means.
If you look at the documentation for FinancialData, you can get ...