So that you don't flood the site with tiny questions but are forced to think things through a bit and only ask a question when you have something big.
We're not a support forum, we're trying to build a permanent repository of good Q&A knowledge about programming on SO.
If we let you ask every minute, we encourage you to use the site as a support forum, and also we fail to teach you to solve some problems yourself.
The world doesn't need a reference to the process of you writing some code, but might be helped by the solution of some of your bigger issues.
It's at the IP-level to stop you working around the limit.
If you get more rep (100) you'll be able to ask more often. To get more rep, try
- Thinking carefully about the best ways of asking questions - a well-asked question with the goal of permanently recording helpful information will get more upvotes than a quickly-typed "what should I do next/please fix my code" question.
- Answering some questions that you do know about.
- Suggesting some good edits to question to dramatically improve the spelling, phrasing or layout.