Trying to analyze market data in R, but companies continually show very low average growth over large time intervals
This simply has to do with the fact that returns are compounding, i.e. the daily percentage changes are cumulative. If a stock gets has a daily percentage change of 1% for a single year (trading for 252 days), and therefore also an average change of 1% the total return over this year will not be equal to 1%. The actual return is equal to $(1 + 0.01) ^{252} - 1 \approx 11.274$, meaning around 1127.4%, which is much larger than the average daily change of 1%. To get the correct total return over a specific period you have to multiply the percentage change for each period, which in your case is daily.