There are many plausible reasons to think 24x7x365 would be bad, for example if you're a person doing your own trading, you can't be awake 24x7x365, so you de facto create intermediate layers of professionals.

To me, as discussed here (assuming you want open capital markets), low frequency (a few times a day or even once every few day, weeks, ...) auctions would encourage people to place long-timed buy and sell orders based on their evaluation of the company traded, rather than short term trends and fluctuations.

Note that in practice traders on currency markets for big banks ("FX" traders) do roll their books from continent to continent each with its own trading team and do nearly 24x5 trading.

Some companies also have their stocks listed on multiple exchanges on different continents (it's called "ADR"), so you kind of have 24x5 trading. Some companies are rolling back those multiple listings (it increase compliance costs and the benefit isn't great any more in the internet age).