They didn't want it to be a website, and if they did make it a website they'd have to deal with the inevitable entitled whining on their Show HN wondering why everything has to be a website these days.
If there's one thing I've learned from a few decades on the internet it's that the only way to avoid entitled whining is to never, ever release anything, especially not for free.
It's literally a free, ad-free app. If it were a website, I guarantee you HN would lambast it saying they could vibe-code it in 1 hour, it's not open sourced, etc. It's never enough for the naysayers.