Manipulation, such as gapping the price higher or lower to make profit from options or increased liquidity of regular trading hours. So you spend $10 million in the pre-market hours to make a stock open 5% higher and then use the extra liquidity to unload a $100 million position at the open while also selling calls.
crypto markets don't have this issue and are open 24/7
Now, we still maintain that for some markets. I'm guessing its a combination of laws, inertia, and the ability to do outside of RTH news/sys updates.
Some markets are open much more than the 9-430 stock market - for example futures markets open sunday night.
A lot of trading takes place in the last 30 minutes of the day for that reason.
I'm sure you could pay professionals to work in shifts to monitor stock prices 24/7.
> because the end-of-day price is significant a lot of things.
Isn't that circular reasoning? "The stock market needs to close during the day because the end-of-day price is significant to a lot of things because the stock market needs to close during the day". Take the spot price at 00:00:00 AM as your end-of-day price and call it a day.
> I'm sure you could pay professionals to work in shifts to monitor stock prices 24/7.
I guess you'd have to pay somebody extra to monitor those prices overnight. And the companies themselves by-and-large are doing less in the middle of the night in their local time. I mean, I know it is pretty detached from reality, but the stock at least tries to pretend that it is in some way grounded in the fundamentals of the companies involved, right? No news, no new info to make trades on.
Another two words: algorithmic trading