Why no specific provision for joint custody?

I'm reading more and more about how my state (RI) has "no specific
provision" for joint physical custody. It's very strange because
neither my ex nor myself is mentioned as the custodial parent on the
divorce decree. We asked for joint legal and physical custody.

I'm curious about this for a few reasons, but for the moment -- why?

What advantage would the state have (I'm guessing there must be one) for
failing to have a provision for joint physical custody? What I've read
indicates that the court wants to see one parent awarded "possession" of
the child.

I'm confused about what resistance my state might have to joint physical
custody, especially since the goofiness resulting from there being no
rules in place governing it has affected me and continues to do so. For
example, even though my ex does not have primary custody, she was able to
get on welfare and collect benefits for our *son* (NOT herself, as she is
on disability), and then CSE stomped in and demanded that I pay the
maximum amount of money allowed by the law.

- Ron ^*^