As a current computer science tutor, I'd say there's a lot more detail and conditions regarding if, and how much, I'd help students for free.
My college pays me for my time spent tutoring (I'm actually on the clock now, waiting between students), but the tutoring is completely free to the students, and I get paid whether a student shows up or not.
When I'm not officially tutoring for the college, I'm still typically happy to help a struggling classmate or friend with their course. However, there is a limit to the extent I'll go, if I feel the effort isn't being reciprocated on their part.
For example, a few of my students (in my official, paid tutoring) always show up having not read the assignment, or attempted to start it without my help. In my experience, this makes for a very frustrating, slow session, where I'm basically talking them through every step of the process ("no, put the semicolon after the parentheses, then press enter"). I wouldn't dedicate any extra time beyond what's required to help these students, as they're clearly not putting any effort in on their own.
However, I'm also a participant in my college's robotics club, and I'm thrilled to work with helping the club members learn to program, as they have a genuine interest in learning, and reciprocate by teaching me when they can (many have extensive experience with metal working for example, but none with programming).
Likewise, it makes a huge difference for a student to come in having already attempted the problem, and able to describe the specific issue they're stuck with.
It also helps a ton if they're just being generally friendly and appreciative of my help (pretty much all students are polite, but some just stand out for their sheer friendliness).
Regarding a theoretical unpaid service for helping others, I'd likely be happy to contribute to such a project, except for the fact that I know I'd end up far too much time on it, it's just too hard to say no to a struggling student. I learned very quickly why my college tutoring center policy is to not give your contact information to students. It's nice to be able to help them, until they're pleading for help preparing for their finals, and you have your own finals to focus on!
By the way, I haven't looked into it too much, but I believe there is a community that sounds similar to what you're describing, in the r/programmingbuddies subreddit.