Well, the argument "since Ruby is not as heavyweight as Java or C++,
there's no need for an IDE, I've been doing well with simple editor
X!" is flawed for me.

I've been doing Perl with CPerl for years, and Ruby with TM for
years. There's still room for a ton of help. There's a negative space
you don't see out there. That's why people come with plugins, because
once you have the help of snippets, or once you know how helpful is
being able to jump from action to view, or from model to test case,
then you value that and want that extension.

Your reaction is not: "Ruby is simple, I can type
validates_presence_of myself no prob". Your reaction rather is "ah,
albeit Ruby is simple, that's still helpful!". That "ah" moment
happens a lot working with a Rails-aware editors like RubyMine. The
first day I saw renaming a controller renamed all the folders, tests,
etc. for you and updated the repo with the changes if you wanted, I
was sold. The day you make a typo in the table name of add_index and
gets underlined in red, you say "ah, Ruby is simple, but that's
helpful". And same with a ton of Rails-specific features (have little
experience with Ruby-only projects in RubyMine, there's support but
have not used it).

If you could have those features in Vim you'd like them. People prefer
Vim in spite of not having them because in their pros and cons list
they value other stuff. Like being able to use it for everything (I
can't do Perl with RubyMine), extensibility, speed, memory usage, etc.
I understand that and that's fine of course.

But saying "Ruby is simple, we do not need much help" is flawed, when
you get help you value it. And that's why people install a dozen
plugins, to get as much help as possible. (And sometimes people don't
because it gives the feeling of an aggregation of stuff to some and
prefer a lean environment.)