I know that meta keywords are not being considered by most of major search engines anymore in their rankings (well, at least this is what search engines (not all!) say...).
However keywords are still an important meta data information about a web page (even if you trust them or not, this is not the question here). And keywords have other purposes besides rankings in search engines, especially in a semantic web perspective. Many web applications and services still use them, for example web directories.
Moreover, I'm sure that a lot of my future customers are still convinced that keywords are an important part of SEO. So why shouldn't they have this option?