In some cases, they patent and make the patent available to prevent others from patenting the same idea and demanding royalties from them (defensive patents). The Patent Office is so overloaded and limited in its expertise that it will often grant a patent to something that should be considered common art. Getting the patent may be expensive, but it could be better than long term royalties, or worse, your competitor gets the patent and then won't license to you.
Slashdot Mirror
In some cases, they patent and make the patent available to prevent others from patenting the same idea and demanding royalties from them (defensive patents). The Patent Office is so overloaded and limited in its expertise that it will often grant a patent to something that should be considered common art. Getting the patent may be expensive, but it could be better than long term royalties, or worse, your competitor gets the patent and then won't license to you.