If-none-match header is not supported when we pass all the cookies even though caching policy says to not include any cookie in cache ke

As per the documentation https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/Cookies.html

If-Modified-Since and If-None-Match conditional requests are not supported when CloudFront is configured to forward cookies (all or a subset).

Why such restriction is in place when I explicitly attached a caching policy to the distribution which says do not include any cookie in the cache key? I want all the cookies to be forwarded to the origin but only include specific cookie value in cache key. Also I want if-none-match to work as I would like to use Etag based functionality for cache invalidation.