In fact the trend is in the opposite direction, towards shorter trading hours as well as more turnover in the opening and closing auctions. Shorter hours especially would be a huge win for work-life balance and diversity in the industry, and just as importly for reducing costs.

Having the markets open longer only spreads liquidity thinner across the day, and moreover having announcements made, corporate actions processed, etc etc is better done when the market is closed so everyone can be on the same page when the happen.