Like everything else in Hollywood, my first movie - "Short Time" --- was made because of a combination of luck, timing, and some shameless groveling on my part. But mostly luck. For once in my life, the cookie fortune was right and the stars were aligned in my favor, not that I believe in any of that crap.
Unfortunately, the stars shifted. The astrology changed. Not in a good way.
It helped that "Short Time" could be made for peanuts --- $35,000,000 - and that people predicted that it had a fair chance of attracting a star or a name director. These are the same people who thought "Death to Smoochy" would get an Oscar.
It doesn't often happen that way on a first sale. Many - perhaps most --- screenwriters spend years developing ideas and rewriting other peoples' scripts that never get made. Most of them earn barrels of lucre doing this, but success eludes them, unless they have a close relative in the business. Lacking that, they are eventually perceived as bad bets and the money train grinds to a halt.