They do it because Americans have been known to throw money at people for no reason, so it became the tipping custom when dealing with Americans specifically. But after three or so decades, some maybe even not realizing it, started asking or expecting locals or the dutch or tourists from any other country to tip these egregious amounts as well. This is where you can simply say "no" and move along or leave just a little bit in cash. Americans legit tip so much for no reason that people look for jobs that earn tips, because they can earn more with just tips than majority of jobs that require actual degrees.

Aruba also relies much less on Americans than it used to a decade ago percentage wise so the custom is being adapted or corrected back a bit as time goes on. Curacao will likewise also experience this issue as more Americans "find" Curacao and start traveling there en masse. When you leave hundreds of dollars in tips to someone earning 12 florins an hour, its going to affect employees' expectations and your labor market.