Why write and submit articles online ?

I can list down 3 significant reasons why. Of course there are more reasons than these 3. But these are likely to be why for most people.

Getting people to read your articles
Of course you want this. But beside providing free information for them, what you really want is for them to check out the links you have put in your articles. Most probably it lead them to an affiliate website. Any purchase there would of course benefit you as you are the one that lead them there in the first place.
But its actually the right attitude, putting links this way only give an option for them to check it out. So you are not really intrusive in your intention. Furthermore, the people that come to your articles are really searching for the information you provide in your articles. So they welcome whatever extra information you can give them even if it is located in an affiliate website.

Getting yourself recognized
You surely want people to know you as an expert in your field, don't you ?
Writing and submitting your articles online can do this for you. But you must of course do your homework and come out with a nice well researched articles. Do not come out with other people's article and claim that its your own effort even with those PLR (Private label rights) articles. Although legally you are not wrong, readers may eventually found that you just "rebrand" the articles to be your own. Once they did that, all your effort even though however true may also be viewed as being "rebrand".
On the other hand, if you managed to put yourself across even if your articles are not top notch ones, they will be eagerly be waiting more articles from you. Then go ahead a publicize yourself an ebook which could be a collection of the articles you have publicized. Although the information you are given are not new, you may be surprised how much impact it will have on the people who are looking up to you as an expert.

Getting paid
Where can you get paid for your articles without having your rights to the articles removed ? Meaning that they bought your articles on private label rights arrangement and made them their own. Sure, you can get $5 or even $20 per article. But then no one will ever know that you are the one who wrote them.
Why not try ArticlesNow4 ?
You may be able to share the profits they made if you are in the top list of original articles contributors and/or articles most viewed for any month. Its an exciting concept that I think you should try. As the website is newly launched, imagine the number of view your articles would have for the visitors there.