I probably just got annoyed with a bot

[AZJonnie]

2. Inconvenient (and BIG waste of resources) but this sort of thing is partly a loss prevention measure

And also minimizes the number of "managers" that must be on call around the clock to make decisions about refunds. Plus of course this way they're also betting on customers being too lazy to send back the original at least some, so more $$$ outright there. Logically I'd intuit possibly some also get better rates with shipping companies they work with for having this policy/MO, because more stuff gets shipped! That could be a whole racket, quite frankly.

The loss prevention side is that larger companies don't want to 'deputize' lower level employees to hand out refunds after the fact (which is what you were asking for, even if it's a credit card, same idea), let alone let bots do so (at least, not for now, that could change). Too easy for employees to rip their employers off is the long and short.

By kicking this whole thing up the chain to the ordering/delivery system, wherein all you as the customer are getting is a DISCOUNT on a second purchase, that's a different liability level versus a refund after the fact. Basically they can entrust lower-level employees (and bots) to effectively facilitate "refunds" via this functionality with less risk. And there might be kickbacks from the shipping companies, as mentioned above.

As an aside, you ever wonder why many stores ask you to sign to confirm you returned something to the store? That's actually because they don't trust their employees.