[maxerickson]

Per IP limits don't do anything about the scenario where the API is integrated into a third party website that sees a sudden spike in popularity. At that point, the API is providing free capacity to the third party site. Maybe that is fine, but you seem to be ignoring the possibility.

[AnthonyMouse]

Because it's fine. That's what it's for, isn't it? The public, via some website, is requesting the government data their tax dollars have paid for.

Which allows that website (or app) to operate with minimal resources, e.g. by a non-profit or open source project, instead of having to be a for-profit entity which needs some underhanded way to generate revenue in order to display the "free" data.