I’ve worked for three cloud consulting shops, they would never allow this. One of those consulting shops is AWS’s internal shop.
Later, when submitting expenses, the upgrade had to be marked as a personal expense, to be netted against per diem or paid back directly.
Early in my career managers did a very poor job of explaining that this was allowed.
I frequently took my wife with me on work trips and we would stay a few extra days. I would buy her ticket separately, have separate receipts when we ate out so I could have mine reimbursed and put the extra days as personal in Concur.
Our favorite chain hotel is Embassy Suites where you got a good free breakfast and an afternoon happy hour with free alcoholic drinks so she would benefit without it costing the company.
Funny enough, since expenses reimbursement approval was done by a department outside of the US, they consistently disallowed my hotel expenses because it showed two people in the room even though it didn’t cost more and was within policy. I just had to tell the hotel only to put 1 guest.
I know the hotel check in thought I was having an affair with someone even though my wife was standing right there with me.
Companies also tend to overlook excessive travel expenses if the employee is bringing home the bacon. But don't put hooker expenses on it! (Yes, I've seen this happen.)
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.
Most likely because they were tired of being defrauded. As usual, it only takes a few bad apples to sour things for everyone.