One would think that there would have been contact in private between a godfather and his godson.
So even though Constantijn and Laurentien were not very often present at international royal gatherings, a private connection would be reason enough to be present at the funeral.

But perhaps the Oranjes have a different idea about the meaning of the role of godfather/ godchild.

I don't (didn't) see my godparents often, 1-2 a year and a few calls and cards/ e-mails throughout the year but if one dies, I will attend (have attended) their funeral.