Matt Levine's theory (regarding Robinhood mostly, but maybe applicable) is that people were bored (no sports to watch, can't go out, no cinema, no pubs), and so

Matt Levine's theory (regarding Robinhood mostly, but maybe applicable) is that people were bored (no sports to watch, can't go out, no cinema, no pubs), and so they started gambling on the markets. Additionally, many people reduced their spending (can't go out, no cinema, no pubs), and many of them retained their income or even augmented it (stimulus checks). So, discretionary income and fewer choices on what to spend it?