Stackexchange vs. a forum
Stackexchange is designed to be an archive of questions and answers - easy to reference, easy to get an idea of useful information. This is very different than a discussion forum, which is much more casual and designed to be an informal conversation.
On a forum, you can ask a question and spend 2-3 pages going back and forth and clarifying what you mean and it's great for you in the moment - it's a complete nightmare for anyone going back to try to get a quick and easy question-answer reference. Because StackexchangeStack Exchange is set up to be easy to reference, you're expected to put a little more time into framing your questions and putting out your answers, so other people can get the value from it easily.
(I speak from much personal experience. A lot of the great RPG knowledge I got came from stuff on the now closed Forge Forums, but, I would never point someone to dig through the archives for an easy idea on anything. A lot of those ideas are basically scattered across months or years of threads...)
Mutuality is your payment
You came to stackexchangeStack Exchange to get some help, right? Presumably you looked around and saw some other questions and answers and decided you'd get decent answers or help here, as opposed to the many, many, many other rpg forums on the internet, right?
The cost of getting thoughtful answers and help is that people expect you to take the time to make thoughtful and clear questions and comments as well.
I make minor typos or formatting errors pretty often, but it's not a big deal because I put enough effort in to show I'm at least acting in good faith to try to make things easy for people to read and digest. I often will take a look at the preview and double check what I've put together to make sure it reads easily enough.
You're right, you're not getting paid to write here, no one else is either. Good faith and a little consideration goes both ways.
Other Possible Issues
If you're working with some situation that makes this especially hard (english as a second language, learning disabilities, etc.) it might help to ask on Meta if anyone can point you to some better resources to help improve things. I know the spell check in the comment box helps me often enough.