This is actually a great idea. There should be a single webpage/site which advertises all major websites and/or brick & mortar joints which accept Bitcoin. Like you said, I cannot think of a site which does this and it would be nice to actually know where I can go to spend Bitcoin if I want to.
I do know that
https://Fiverr.com used to accept Bitcoin (back in 2014/2015), however they discontinued it. I do not blame them either, because it is currently a lot more complicated to both use and accept Bitcoin as payment than traditional fiat methods.
With that said, hopefully it will become easier going forward.