To authors, it appears that publishers (and agents) frequently spend an inordinate amount of time to make yes-or-no judgments on purchasing proposals. As a result, it appears like posting "moves slowly." However, the reason it appears to be delayed is because your project is one of dozens or hundreds on each agent/desk editor's at any one time. They have to deal with many projects at once! Even if your proposal is immediately accepted after you send it in, that doesn't mean the publisher will publish your book within the next six months. They might need more time to secure rights, do research, etc. Publishing is a huge undertaking that takes time and attention from many people. Even if your proposal is instantly accepted, it might still get lost in the shuffle with others that are also being considered at the same time. Publishing delays are common but unavoidable. If you want to know when yours will be published, just wait about two years from the date you sent in your proposal.