It's imporant to pick out vulnerabilities and deficiencies compared to other projects to get them addressed, rather than only say nice things. However, the core issue is that people raising them are usually ignored until there's an embarrassing hack or demonstration (Homakov).
For example, all new gem releases should be signed and `HighSecurity` should be the policy but it's taken years to get very little progress. Changing to that policy would prevent entire classes of attacks, attacks that could subtly inject code into all sorts of apps in difficult-to-find ways. Large projects are still shipping unsigned gems, unsigned commits and unsigned tags. If RubyGems were hacked, progress might move slightly faster.
Rubygems has been lagging behind other packagers like Apt, RPM, NPM, and even newer things like Rust's Cargo. It's woefully overdue for an update.
That being said, there's great services like GemCanary (https://gemcanary.com/) that will read your Gemfile and produce a list of vulnerable packages for you automatically. It'll even email you alerts when there's problems.
The security story in Rails might not be perfect, but at least there's reporting and tools.
Keep pushing for signed packages, though. Long overdue.
You're getting downvoted because security issues are far from unique to Ruby on Rails. Are you aware of any web frameworks with a pristine security history?