This website has been outfitted with the means to detect spam answers in an effort to cut down on the amount of spam posted to questions. If the algorithm put in place deems your response to be spam, it will cause your answer to be invisible to other respondents, but you will see it under the question. This happens for a number of different reasons, namely - because the algorithm has determined that your response has been copied and pasted, i.e.: you've given the same response to a string of questions; because your response contains a hyperlink (these responses are flagged because many spammers use them to provide links to websites in an effort to scam people); or because your account has received a number of reports from other users and your answers are being held back until it can be confirmed that you are not continually posting content that goes against the rules of the site. Another common reason is that your account has remained inactive for some time and the algorithm sees renewed activity as a suspicious spike and immediately regards it as spam. Recently this site was hit with a flood of spam from multiple accounts and when the users didn't go anonymous, it was clear that they had opened the accounts some time ago - quite a few were several months old. They did this in the hope that they would be able to fly under the radar because most spam accounts are operated by people who try to get as much mileage out of them as possible before they're shut down. These spammers thought that they could extend their shelf life by accruing a bit more time in the hope that they would initially be seen as legitimate accounts. The 8 character point gaming was designed to build up enough points to ask dozens, scores, hundreds of questions before being terminated. Thus, the 15 character limit was also put in place.
A better question would be: "Why are you maintaining two accounts to begin with?" It's true that maintaining two accounts does not directly go against the rules, but having them interact with one another does. The honor system put in place requires that any user who possesses two or more accounts is not supposed to access the same question with two or more of them. If you've already answered a question, then you shouldn't be viewing your own answer with a secondary account because there's nothing stopping you from up-voting your initial response. And if you've asked a question with one account, you shouldn't be posting an answer to that question using another account either. This was once a very prevalent problem, so the system was re-calibrated to ensure that users could not give themselves a best answer when answering their own questions anonymously.