As a reporter, if I can't find where to report it, you'll find out about your issue when someone forwards my blog post to you. If you ignore my e-mailed report because you don't want to spend the resources on it, e.g. because I haven't built a reputation score, same thing.
Most importantly: If the only way to report a security issue is through a platform with a "community managed reputation score", I'm much more likely to ignore that platform and again, you'll find out about your vulnerability from a blog post.
security.txt actually told me about a contact address for Cloudflare that isn't HackerOne. (HackerOne, in particular, is on my shitlist because they impose terms of service that deter disclosure unless the vendor agrees, and they don't let you publish through their platform if the vendor is unresponsive. If the only way to report to you is through HackerOne... see above.)