I don't think this is an EU vs US issue or an arbitration issue. Even if every dollar you spend while traveling is reimbursed, you don't really get compensated

I don't think this is an EU vs US issue or an arbitration issue. Even if every dollar you spend while traveling is reimbursed, you don't really get compensated for the non-monetary annoyances of traveling. You might have to fly at weird hours and be tired or jetlagged, and you miss a few nights away from your family. Maybe you're traveling during the work day so you are being paid for that time, but you might have had to wake up earlier than usual, or sit in traffic on the way to the airport, or all kinds of other things that aren't compensated by the company. Even if nothing does go wrong, traveling is still somewhat stressful for a lot of people just because you're aware of the risk that something might go wrong. Not to mention the fact that you're forced to lend the company money for a month or two at 0% interest. If you have no problem with this imbalance between the company and employee, that's great for you. But IMO it's very easy to see why employees are incentivized to stretch their reimbursements as far as possible to help make some of it back. It's hard for me to see this as morally repugnant.