Maybe professional trading firms can't convince their highly-paid trading, development and support staff to work weekends? Nobody wants to be the guy that lost

Maybe professional trading firms can't convince their highly-paid trading, development and support staff to work weekends? Nobody wants to be the guy that lost $AWESOME_EMPLOYEE_X to $BIG_COMPETITOR because they forced him/her to work weekends. This would change if more retail investors joined the market, because they're at least as likely to trade during weekends, and if there were enough of them then professional firms would be a relatively small proportion and the effect of their trading hours less noticable.