Wow, never heard this, maybe this is the case in some places in Southern Europe. But in the North these jobs at the ports authorities are definitely good paid and attractive jobs. Same with airport lugguage, that is (one of) the reason why the passenger and airline fees at these airports are so high.
Almost the same situation here, in Germany, Belgium, Holland, France ... these are very attractive jobs with high salaries. Not to speak about Norway and Scandinavia.
Actually the least people I would tip are people who work for the (air)ports and tour guides, they probably earn more than me 😄 And they deserve it, no question about this.