There are many reasons to sell an altcoin right at the very bottom. most of the altcoins loss their price very fastly and it is very difficult to predict the low price. After losing the price, the trade volume becomes very low. On the panic sell, people lost their patience and sell their altcoins right at the very bottom.
From now on, altcoins will increase gradually, till the end of this month, or till the end of the first two weeks of next month (August). From that, I believe that altcoins will officially start their bull run, the second bull run for altcoins in 2019. Altcoins have nearly come to their endings of bearish period. If you noticed, their volume all increased considerably recent weeks.