Because one, it's kinda rude.

How do you just accidentally buy something.

When there are multiple confirmation pages.

And then decide after the order goes through and you've made the person very happy by making a nicely priced sale only to dash their hopes and dreams by demanding a refund.

Sorry but I'm gonna let you sweat it for a bit before I confirm the cancellation

Thanks for making me believe I made $85 I could really use right now.