Hi, @slc! Thanks for your patience and welcome to the Vercel Community 
I’d be happy to provide some information with some resources to help address your question about static Next.js App Router apps generating ISR Functions.
ISR (Incremental Static Regeneration) for static pages
The behavior you’re observing is related to how Next.js and Vercel handle static content optimization. Even for entirely static sites, ISR can provide benefits in terms of caching and edge distribution.
Vercel’s Data Cache and Edge Network
Your intuition about the ISR functions living on the Edge and caching static data is correct. This approach allows for efficient content delivery and reduced origin requests.
Fast Origin Transfer (FOT) and Fast Data Transfer (FDT)
Your understanding of FOT occurring once per deployment for static content is correct. The Edge Network caches the content, reducing the need for frequent origin requests.
Bandwidth and usage concerns
Regarding your concern about surpassing the FOT limit, you’re right that for static sites, the transfer to the edge occurs once per deployment. This means that the 100 GB limit is unlikely to be a concern for most static sites.
Next.js App Router and static optimization:
The App Router in Next.js is designed to work seamlessly with both static and dynamic content. For static sites, it still leverages ISR for optimal performance.
In summary, while it might seem counterintuitive to generate ISR Functions for entirely static content, this approach allows Vercel to optimize content delivery through its Edge Network, providing better performance and scalability for your application.
If you have any further questions or need more clarification, feel free to ask!