Chase probably does not know if it is a routine, allowable transfer or against the rules at the time you initiate it. Better to warn everyone, every time, so there is no "well you never told me I couldn't transfer to my uncle's girlfriend's goldfish..." argument later.

They also want profitable customers. Closing a card the instant you hit minimum spend is not profitable for them. Same with charging $20K a week in gift cards at Staples to get a 5X points that costs them more in rewards than the merchant swipe fee makes up.

I am sure that those exact same terms are in the T&C booklet that came with your card, but nobody reads that. Putting a simple popup on a website probably saves 1000s of hours of time for CSRs arguing about why abusers had their points taken away.