Shareware is a marketing technique, not a breed of software. It is intended to put inexpensive quality software into the hands of users, allowing them to try the product before they put their money down, much like test-driving a car. The cost is kept low by letting users help with the advertising and distribution, eliminating two major expenses of publishing software. Shareware distribution offers benefits to users and authors alike. Users can evaluate software on their own systems before making an investment.
Costs are typically much lower than for traditionally marketed software of equivalent functionality.
Authors can bring their software to market with very few start-up expenses while maintaining complete control over development. And software quality improves through the close interaction between creators and users. But shareware is not intended to be free. Free software is great, and the authors who place their works in the public domain, or who keep their copyright but allow unlimited free distribution, deserve to be thanked. But that's the authors' choice.