Why does the PH say if a trigger occurs you can ignore it?

@JeremyECrawford Why does the PH say if a trigger occurs you can ignore it? Wouldn't it be better to include "…and wait for the trigger to occur again"?

— Tyler Ryan (@TySQL) May 8, 2017

Ready action. The rules says you can ignore the trigger, because yes, you can ignore it. You can try again if it is open-ended enough. #DnD https://t.co/GFdvm94iMX

— Jeremy Crawford (@JeremyECrawford) May 8, 2017