I think it depends on where the bottleneck is, and what they’re actually trying to prevent, as to whether or not rate-limiting would actually help anything.

If they are blocking source IP addresses explicitly, it could be for a more specific concern we’re not aware of, like trying to limit the amount of email “spam” that would be sent out from automated requests. A rate-limit wouldn’t fix that issue, only slow it down.

We’re all also assuming any of this is even intentional on their or anyone’s part.