That's interesting. It might be generational difference: as a kid and teenager, I grew up voluntarily helping other kids and adults at a sport they weren't experienced in; even though they weren't able to help me, I still felt happy helping them.
Also, in almost every other forum I've visited or been a part of, the mods and other experienced members who volunteer their time and aren't being paid, don't mind helping new people or answering their questions, even when it's their first post; as a result, they usually stick around, even if for a while.
But, if they leave or don't stick around, the mods and other forum members don't stop helping new members; we enjoy helping young teens or adults who are confused and don't expect or demand that they attempt to help others first before responding to their question(s) because they might (and do, sometimes) end up giving others incorrect advice that isn't scientific or factual (then, the other forum members have to chime in with the correct information). Plus, we don't think of it as being useless if they don't respond, because, with the information posted, it might end up helping future people who visit the site, and then, might reduce the number of questions new people ask.
To give an analogy, it'd be like asking a first grader to critique an eighth grader's homework; unless the first grader is a prodigy at a subject the eighth grader isn't good at, like math, for example, then the first grader's advice won't be as helpful or as useful to the eighth grader.
Perhaps, that might be the reason why new playwrights don't feel comfortable participating in critiquing others' work: they are inexperienced and don't want to give others wrong information or help, especially in a field that is subjective, like playwriting. But, not all playwrights are looking for others to critique their work: I'm not.