Changing "examples" on a website

On my homepage, I have a very simple design (think Google, but for numbers) with an input box that has a placeholder giving example inputs one might think of entering. This suggested input changes randomly each time you reload the page, hopefully to give new users a suggestion on where to start or older users a search result that gives interesting results.

However, I never see this functionality on other websites, even though some I feel it might fit well. Take the OEIS, they put an example sequence you can try on their website but it never changes, always staying the same.

My question is if there is a reason why I have never seen a website do this before such as it being confusing for the user (or whether I just haven't found any).