Yeah I’ve noticed it. There’s several reasons I think, some good and some bad:

• upbringing

• can’t be bothered in their old age

• losing eyesight causes them to miss seeing drops after the fact

• wrinkly plumbing tends to make fountains instead of streams

• can’t bend to clean up, because of bad backs/legs

• shaky hands and bad aim if very old

• revenge for not cleaning up after your messes when much younger? 😂

They are images with no background, and the pdf/image wasn’t set up properly to fill that in with the page colour.