In what ways do these decrees illustrate the desire for reform within the Catholic Church?
There are some scholars such as Christopher Haigh that argue that the council of Trent should be called the Counter-Reformation. This point of this title is to underline that the Catholic church would have had a reform with or without the Protestant Reformation. There were a number of elements that required reform and it was taken care of, such a the idea of selling indulgences. Recall that Martin Luther revolted against John Tezel's slogan "A coin in the coffer rings, a soul from purgatory springs." To address this abuse alone was a great work of Trent. It also gave more unity to Catholic doctrine. They did not necessarily change doctrine, but made their doctrine clearer. This was perhaps the most important aspect of Trent. Vatican II did not change much either.
To me, it's not completely clear that the Council of Trent really illustrates a desire for reform (at least not in the sense that Martin Luther thought the Church needed to be reformed). Instead, the decrees do more to reassert the rightness of the Church and its doctrines.
There was only a little bit of what I'd see as reform -- the banning of the sale of indulgences and the requirement that priests be better trained.
On the other hand, the Church affirmed the rightness of all its major doctrines. It also reaffirmed and even increased the power of the pope. So I'm not sure that the Council really did illustrate a desire for reform as much as it illustrated a desire to restore the power and authority of the Church.