One of the benefits of straight-to-DVD releases is a reduction in marketing costs. Marketing costs for a theater release film are not at all insignificant. It wouldn't take a great deal for a theater release movie to spend thirty million dollars in advertising.
Consider that virtually every theater release film is advertised in some form of print media, and often on television as well -- mostly at so-called prime time hours, where the greatest reach occurs but where costs are also highest. And costs for television advertising can be astronomical. The cost for a Super Bowl ad is at the million dollar level. Given that, it's not at all difficult to envision spending three hundred thousand dollars for one, one, thirty-second ad spot on a prime-time television show that has a good market reach.
The straight-to-DVD film can spend on advertising, but it's not especially typical. In most cases the main form of advertising for a straight-to-DVD movie is its box cover. The DVD box cover sits on a shelf in a video franchise store, customers walk past, see the DVD box, make some form of a choice about the film, and make a purchase or not. This is why having a name actor can be critical to a straight-to-DVD's commercial success: the name actor serves as a selling point, and will be always featured prominently on the DVD box cover. This sort of leverage makes for potential profit points in addition to a salary.
The screenwriter for a straight-to-DVD production will likely see no profit points, and will receive a lesser salary than the screenwriter writing for a major theater release film. This should not be seen in a pessimistic light. Writing a script for a straight-to-DVD release that has a good amount of push behind it will generate a pay of tens of thousands of dollars, at least. It will additionally be a career achievement, and career achievements always count in getting further work in Hollywood -- and in every other industry for that matter.
Being a screenwriter for a straight-to-DVD production also means becoming part of the straight-to-DVD market. The reality is that straight-to-DVD movie making is a profitable industry, and the proof of this is that straight-to-DVD movies are still being produced. In the entertainment industry if there is no profit, there is no product. The writer who writes the script for a straight-to-DVD film is a member of a profit industry, and gets access to all the perks that go along with that.