General question about trivia

I have a general question.

I've submitted hundreds of trivia contributions over the years that have been approved on many movies and TV programs.
But time to time I will revisit the trivia section where made those contributions months or even years ago and I've noticed sometimes they've disappeared. I'm curious why they are taken down when they were first approved by IMDb. 
In the end, I end up resubmitting that same trivia again anyway, where it usually gets approved again. The funny thing is, I may go back much later to see if it's been taken down again. It's almost become a game.

Can you tell me why this happens?