Also, everyone has harped on the higher fuel burns.
What no one considers is that fuel has far lagged behind inflation in price, while salaries have not.
As that trend continues it becomes more and more profitable to burn more fuel to reduce flight times.
Crew productivity is already at its limit. You aren't going to get below two pilots or 1 flight attendant per 50 pax so the only way to reduce salaries is to go faster, even incremental improvements in speed could help the airline's bottom line.
Cheers
Wino