If I was deemed disabled by Social Security, why do I have to fight to get my disability from the state?

I do not know the answer to this question. This is not an employment law question.

It is impossible to answer your question other than to state that it does seem illogical. The problem is that a determination of disability depends on the definition of that either by the governmental entity or an insurance provider, including the fact the disability may be defined differently by the state and the federal government.