At Schiphol they offer tipping options to presumably prey on Americans, but the attendant physically reached over the counter to reject it after I ordered in (native) Dutch. Can't imagine how much trouble locals had been giving the shop before training staff like this.

Happens in Spain too, the card machine will sometimes have tip options but the waiter selects no tip if serving locals to avoid the annoyance

I’ve seen Starbucks employees in the US do this often.

Isn't this directly taking money out of their own pocket, or are tips going to corporate?

What takes money out of their pockets is not paying a real wage for a real job. TIP destroys the value of a profession and when you don't think a profession is 'professional' you pay less for it. This is a terrible dark pattern at every level.

I am not arguing for tipping culture, but I question the incentive for rejecting a tip as a US Starbucks employee. I very much doubt that playing a part in desired society-wide change overcomes the immediate incentive of the tip itself.

I don't go to starbucks personally but I've been to local ice cream shops, Cafes, fast food businesses, and others and this isn't too uncommon. I'd say it happens about 15% of the time? Its usually at places where tips aren't as expected anyways, but not always.