The three companies have travel policies that apply to everyone. It also depends on who is paying I guess. I am a post sales consultant where for the most part, my company gets reimbursed by the client and in the contract, they have the guard rails as far as allowed travel expenses.

Then on the other hand, you don’t have to choose the cheapest airline possible, so you can choose the one where you have status and get automatic upgrades (Delta Platinum Medallion in my case) and a higher chance for upgrades.

Of course you can pay for the upgrade yourself. But why would I spend my own money to do so. They are so strict though that every time my receipt after flying showed I was in an upgraded seat, I had to also send in the email as proof that my upgrade was free because of status.

> They are so strict though

Most likely because they were tired of being defrauded. As usual, it only takes a few bad apples to sour things for everyone.

When available trans-Pacific, I did sometimes use miles to upgrade to business (and generally paid the co-pay myself). Pretty much always flew my usual carrier (United) when that was an option.