The UNIX & Linux site is part of a larger Stack Exchange network, and as such uses many of the same settings & processes. There is a Meta Stack Exchange post, Why do I need 50 reputation to comment? What can I do instead?, that describes the reasoning behind requiring 50 reputation points:
We realize that new users may have valuable comments, and that we may lose some of those contributions by requiring 50 reputation points to unlock the feature.
However, history and experience have shown that the downsides of allowing everyone to comment are far greater than a few useful comments lost:
There are big problems with spam. Automated filters cannot catch all of it.
Even among the real comments, most would either say "I have the same problem" or "I agree". Such comments do not add any value, and have to be manually removed.
Comments are very painful to moderate. Stack Exchange sites have a process of community moderation (voting, flagging, review queues) that works great for questions and answers, but not so much for comments. Comments cannot be downvoted or closevoted, nor searched (nor do we want that).
Comments are second class citizens on the Stack Exchange network, not designed to hold information for all eternity. They may get cleaned up at any time. Generally, truly important information should be incorporated into an answer anyway (either by posting a new answer, if the information answers the question at least partially, or by editing an existing answer, if the information is a minor complement or clarification of that answer).
The same post also provides guidance if you want to provide an Answer:
Answers don't have to be exhaustive or infallible, they just need to try to answer the question. It's perfectly fine to post an answer saying, for example, "I'm not sure what the cause of your problem is, but if it's X, you can solve it by doing Y. If that doesn't help, try Z and let me know what it says." Also, if further information does become available, you can edit your answer later to make it more precise. This is a good habit to get into even if you can comment!
On busier sites, if you cannot even try to answer without asking for clarification, then move on to another question. Many new questions are asked every minute, and there are many unanswered questions still waiting for your help. You might feel bad about abandoning the question, but it is the absolute responsibility of the asker to include all relevant information, presented in a clear manner. Failure to do so at any level decreases their chances to find a good answer to their problem.
I'll add my own perspective to this last section: this site has enough visitors with enough reputation, so requests for clarification usually come along shortly. If you have a concern about the question, someone else likely will, too. I suggest staging an answer (possibly offline) based on some reasonable assumptions; "starring" the question as a Favorite to make it easy to rediscover; and then moving on to other questions. Revisit the original question at your leisure to see if it has been edited with updates and consider posting your own Answer. As the Meta post also says:
Asking good questions and providing good answers will get you 50 rep points in no time. Alternatively, you can suggest edits that improve existing questions and answers. Each of those will gain you 2 reputation points.
... and you won't have to worry about the reputation limit for very long.
