This is not true, I've posted so many comment and did not get upvotes, it doesn't mean the answers are trash you should know that the musing.io team has moderators and curators and some of the times it may be difficult to miss a question, I don't agree that any comments are trash or that they don't have enough SP.
Musing is a growing dapps and another things is more engaging and quality comment needs to be rewarded, sometimes priorities are placed and this may mean the curators having to choose between the comments they think have more value.
It's functioning on a limited SP but I believe if you take time to engage and to make impacting comments, you'll get rewarded