This is another duplicate for boardgamearena.com/bug?id=34465 , please don't create multiple bugs about the same issue, just add comments to the existing.

See the explanation there, my assumption is this rule is there to mitigate the fact that statistically, with normal distributions and most played hands just won by the playing team, the starting team always has a small statistical advantage of reaching 1500 points first.

Now, since there is no single source of truth for these kind of century-old public domain card games, I am willing to accept this is just another one of those regional differences (like jokers in the draw pile or not).
Although it is also entirely possible that whoever tought you Klaverjassen just never explained this because it is a very exceptional situation ;)

Someone already started a poll about this in the Klaverjassen forums, but I guess nobody has seen this because it didn't get any feedback.
I will create a new poll later and post about it in the Klaverjassen players group, and see what we get.