I was not the one who made this decision, but if I were I would have the following reasoning. What would you reply with? Would it be personal information about your qualifications or personal contact information? If so then there is no good reason to reply. On the NI side there have been several times someone posts a job and people reply by attaching their resume. This puts personal information like their address, date of birth, job history, references, and contact information in public view where spam bots crawl (among other bad things that could happen).
If you want to contact the poster, then send them a private message, or contact them through the links they may provide.