Americans tipping abroad while on holidays ruins service for everyone that isn't American – as a non-American you are guaranteed to get worse service than a American in touristy places (and sometimes, to add insult to injury, your own local places), because an American tourist will just insist on tipping 20% or more in places where maybe 1€ = good tip and 2€ = great tip. It doesn't matter if they repeatedly get told not to do it, American tourists keep insisting on doing it to "be nice".
The result is that hospitality obviously optimises for being extra nice to Americans and treat everyone else with apathy. And because you only tip at the end, it doesn't even matter if you were willing to tip like an American, you're going to get the bad treatment (and by then when the bill arrives any motivation to tip well is gone – a classic catch-22). You're basically discriminated for not looking and speaking with an American accent everywhere you go as a tourist.
Please, inform yourselves of tipping cultures when you travel and do it appropriately. Also take in consideration a lot of "this is how much you should tip" guides online are horrible wrong and err on the side of overstating the tip (no idea why – possibly not to offend US sensitivities?). You'd think with all the "cultural appropriation" and "cultural imperialism" awareness these days people would be better in not imposing toxic parts of their culture elsewhere, but here we are.