Apart from them being greedy.
Why do some people always remind people to accept their answer?
It's not being greedy. You take some time of your own to help someone in need and it's only natural to be compensated for your troubles. You didn't have to help that person, but you did anyway, and that should be worth at least a little something.
Users are supposed to accept an answer if it helped solve their problem, but a lot of them today won't, hence the need for a reminder. The system has become twisted, as if it was now a competition. Everyone wants to be "the best" and have more reputation than others, and thus askers won't even accept or upvote answers because that's helping competitors, and also because they're selfish and only care about having their question answered. You see people whining in comment sections for being downvoted by other users and flagging questions as inappropriate for no good reason. That's not what Scripting Helpers is supposed to be. It is intended to be a place where users can keep improving by supporting each-others. The idea is to help each-other find solutions to their programming-related problems. Reputation is only a little compensation for your troubles, and also to an extent serves as a way to identify a user's ability to script and answer questions.
Scripting Helpers isn't the only website of its kind. Websites like these are known as Q&A websites, and the idea behind them isn't new at all. If you want another example of a Q&A website, look at StackOverflow. These websites exist for you to be able to quickly search for a solution to a question that hopefully someone has already asked before you. If you ask a question and find a solution to your own problem then you're supposed to answer your own question yourself such that future visitors can benefit from it as well. It's all about supporting and helping each-other.
That being said, with the age group targeted by our website, the questions asked by our users aren't of very good quality. Our questions tend to be too specific to be of help to anyone else but the asker. Normally on a Q&A website these question would be closed as "Non-Constructive", but since that would mean closing literally all questions asked on Scripting Helpers, we refrain from doing so. We also wish to keep the moderation of the questions in the hands of the members of the community, and not of staff members.
Additionally, I'd like to take this opportunity to remind everyone that the "report" feature exists for questions that are in violation of our community guidelines, not for badly written questions, spam, or for complaining about being downvoted.