Because there is a lot more plumbing involved in buying and selling equities or moving money than there is to send and receive email.
Specifically, a lot of measures to prevent something going wrong, because the the damages are far greater when moving things of great value than an email.
You technically can trade stock on a Saturday, just not using all the aforementioned plumbing of a popular stock exchange and brokerage. And you can move money on the weekends, just maybe not with the help of banks because they consider it not worth their while to offer the service on weekends.
Specifically, a lot of measures to prevent something going wrong, because the the damages are far greater when moving things of great value than an email.
You technically can trade stock on a Saturday, just not using all the aforementioned plumbing of a popular stock exchange and brokerage. And you can move money on the weekends, just maybe not with the help of banks because they consider it not worth their while to offer the service on weekends.