From my level of Rails experience I can kinda understand this choice, but my newbie and I were initially baffled that nothing we changed in a system test changed the output of rails test.
At the least, it would be nice to have some indication that system tests aren’t being run by rails test.
It would also be helpful to have a single command for all tests instead of rails test && rails test:system.
Yeah, we don’t run the system tests, because they’re generally slow. We tend to primarily run system tests at Basecamp as a CI step. But this should be obvious. Also, I like the idea of rails test:all which would run both regular tests and system tests together 
Seeing this as a good first-time-contribution, I opened up: Adds a rails test:all rake task by codergeek121 · Pull Request #39221 · rails/rails · GitHub
To get around this I usually modify the Rakefile to include task default: ["test", "test:system"]… So all tests are run with just rake. Not so descriptive though!