Long story short - the company that owns the bridge does a fine job with it. They'd like to build another one, using no tax dollars, subsidized by tolls. The Democrats and the governor want to build it with public money, and so they won't let the Ambassador Co. build a bridge.
The Republican legislature voted the bridge down hard, so now the governor has discovered a way to bypass the legislature.
http://www.mlive.com/news/detroit/index.ssf/2012/06/report_snyder_to_bypass_state.html
And if that's not enough, the GOP legislature, which ran lots of ads mocking the Democrats for the failure of the film industry subsidies, just introduced a bill creating a $100 million film subsidy.