Perhaps because his subjects (subversive at the time and who were his greatness) became common for this time. Alcohol, death, depravity, criticism of the Empire and the Church have much more subversive today (let's not be silly, that one agrees or not with critics do not have a late fight, consider the actual subversion ...).
Baudelaire praised today as he was on trial in 1857, ask you about the evolution of the company: the world is a "dialectical totality" (insiders will understand ...).
Nevertheless, it is a great poet, full of talent and that's why it deserves to stay, but why others are forgotten?