Why is it that companies cannot copyright game mechanics, but can patent them?

Question

For example, the dialogue wheel from Bioware, or the Nemesis system by WB.

In: 71

Answer 1

in order for something to qualify for copyright protection, that something must exist in a tangible form

Ideas, methods, and systems are not covered by copyright protection.

According to the US Copyright Office, Circular 2, this covers quite a few things including:

Making, or building things
Scientific or technical methods or discoveries;
Business operations or procedures
Mathematical principles
Formulas, algorithms
Any other concept, process, or **method of operation**

the last one included game mechanics