After reading When does the Pope speak ex cathedra? I became curious and searched for a list of statements, but couldn't find one.
Does such list exist and if not, why is this the case?
There is no canonical list of infallible statements made by the Pontiffs: while there are only a few instances where a Pontiff spoke infallibly ex cathedra (an extraordinary action), there are many times where he is speaking about things known to be infallible of the ordinary and universal Magisterium.
To the extraordinary sense—when a Pontiff speaks infallibly ex cathedra—there two officially recognized cases.
First about the Immaculate Conception by Pius IX:
But there may be other instances before Pius IX's pronouncement in 1854 about the Immaculate Conception, not officially mentioned as infallible ex cathedra pronouncements, that count: Wikipedia has one possible list. As Wikipedia notes, because of the scrutiny an ex cathedra statement would get, the Vatican has taken to clarifying when a statement made by the Holy Father is, in fact, is an infallible statement done ex cathedra, and it hasn't happened since Pius XII's pronouncement about the Assumption of Mary.
In the ordinary sense—when a Pontiff speaks about things that are known to be infallible by the ordinary and universal Magisterium—it gets a little tricky. Then Cardinal Ratzinger, prefect for the Congregation for the Doctrine of the Faith (now Pope Benedict XVI) mentions in his Doctrinal Commentary on the Concluding Formula of the Professio Fidei about the case of euthanasia:
In a nutshell, the ordinary and universal Magisterium teaches us certain things are evil, and while there may be no mention of a new issue (because it hasn't come up before), the ordinary teachings of the Magisterium can still guide infallible teachings about the new issue without speaking infallibly ex cathedra.
And this happens pretty often: one of the main roles of the clergy, including the Holy Father, is to help guide and instruct based on the ordinary teachings of the Magisterium.
Yeah, you want:
from TAN Books.
It's got a pretty well sourced index. Mark Trapp speaks truth about the Marian Dogmas, there are four of 'em but only the last two are the products of papal statements, the other two were pronounced as result of ecumenical councils.
But, Bl. John Paul II spoke on an infallible teaching about women in the priesthood, that's pretty new so it may not have made the cut for the book. Also, infallibility is defined as the Pope in Communion with the Bishops. So, magisterial teachings are just as infallible as the Popes. Which is why you'll find a lot more stuff in that book than just papal decrees.