Currently you have to exclude non HTML routes from static caching manually. It might make sense for Statamic to exclude those routes by default, since those cached routes return the wrong headers anyways which can lead to issues.
For example if you have a robots.txt route and don't exclude it from static caching, on production it will return HTML headers and a 404 status, this causes Google to shout at you in their Dev Console. Same issue with a site.webmanifest route you might have.
Currently you have to exclude non HTML routes from static caching manually. It might make sense for Statamic to exclude those routes by default, since those cached routes return the wrong headers anyways which can lead to issues.
For example if you have a robots.txt route and don't exclude it from static caching, on production it will return HTML headers and a 404 status, this causes Google to shout at you in their Dev Console. Same issue with a site.webmanifest route you might have.