The correct answer to this open question is the following.
Lower percentages of bills passed in the last few sessions reflect the increasing dominance of conservative legislators who support the idea of having fewer laws and limited regulation in the state Congress.
Conservative legislators that basically are part of the Republican Party, do not support the idea of increased taxation to create a social program aimed to help poor people and the ones in need. On the contrary, they are in favor of fewer taxes so private companies can invest their money in the creation of jobs and the support of investors that can invest their money in projects to promote the US economy.