Maybe Taxes have something to do with March being a negative month for Bitcoin. It was positive in 2019 because 2018 was a bearish month. And 2013 was positive also but back then I don't think there would of been too much tax selling from 2012 loses. BTC had a good year that time but I don't think it made people super rich.
This is one thing which caused a huge crash in 2018 because people didn't realise how much they would owe in capital gains taxes. Basically every trade is taxable whether you withdraw or not. People probably assumed if they don't withdraw, they don't owe. However people made great gains, sell, made a taxable event, then bought something else, new tax year started, and that new alt ended up losing them money, so money was lost but taxes were still due on the 2017 gains. Hence people had to liquidate their BTC to pay for taxes.