So that employees don’t try to avoid critical business travel.

When Apple started flying engineers in business class to China, suddenly they got dramatically more likely to go to work out production issues rather than trying to convince management that the issues would work themselves out. A few million dollars in employee travel was immaterial to the increase in production reliability.

My prior company had a policy that all flights greater than 6 hours were business class flights.

There were a few reasons - there are health issues associated with flying packed into a coach seat. Employees who have to fly a lot for work, if it was requested they fly in coach, might decide to leave their jobs pretty quickly if they couldn't fly business. And, somewhat related, it's considered a "soft benefit" (and 100% non-taxable benefit by employees in the USA) being able to fly business, stay in five star hotels, and have a reasonable ($100 or so) per-diem when engaging in business travel.

You arrive and(generally) go straight to the office. You want your employee to be rested and productive.

Generally it is to ensure their employees are well-rested ahead of the important meeting if it is a very long flight. Add in frequent flyer programs to reward an employee’s airline loyalty, and many business class seats are free upgrades for the employee. After a while, it really becomes a consolation prize.

If your company "always" buys business class tickets for employees, that includes buying business class tickets for the most important person: You