Why is Greenwich Mean Time used in the MySQL database?

I am using a database that inserts data into the database using: Beijing Time-28800 = Greenwich Mean Time (Greenwich Mean Time is 8 hours and 28800 seconds different from Beijing time because Greenwich Mean Time Zone 0, beijing in 8 time zone)

If the website is only in China, you do not need to use Greenwich Mean Time. If it is an international website, you can add different time zone differences to the output in different countries, the local time is displayed. Therefore, for my website in China, using Greenwich Mean Time (input database, and back-and-forth Calculation During output) is an option that outweighs the loss.