New members are restricted to prevent spam, after a certain number of posts the restriction will be lifted.
As for member not replying I can only say that not every post is always read, and if it is read it may not be read by someone that can help or it is read by a nonmember.
When we talk about more and more post are apply on one site is call robots. So it best way to protect your domain and apply limitation for 24 hours post. Now a days search engine work in this method and stop marketing scam. Google update also related to these type of method.