Ok, let me rephrase what I wrote...
Why couldn't the Protestant reformers see the illogicalness and self-refuting / self-contradiction of sola Scriptura? ........... The Reformers had to supplant the authority of the Church with something. That something was the Church's Scriptures. Not only was their doctrine self-refuting, but history demonstrates it is also untenable because almost immediately after the genesis of Protestantism, it began rapidly dividing because this doctrine they built their religion around is not able to resolve any doctrinal disagreements. By the end of the 16th century, there were already nearly 300 different sects.
To me, Sola Scriptura in effect says that the ecclesiastic body that is the church has no authority unless what it pushes is in lock step with what is written. When there is a conflict, go with scripture, and where scripture is silent, believers are unbound by doctrine no matter what their respective denomination promotes.
If we do not subscribe to the above then I have some questions:
Is Sola Scriptura a reasonable stance to take?
Should believers be believers in what the scriptures say more than they believe what their church practices?
Are the scriptures too antiquated to keep up with an evolving would and are churches better suited to be promoters of doctrine than the biblical texts?
As it relates to my understanding of your point that the scriptures came from the church, I must say that I am not sure that's accurate. The full text of scripture likely had been pinned by the mid to late 1st century. The official ecclesiastical Catholic model got its legs no earlier than the 2nd century well after the scriptures were all already in circulation. Over the centuries the church did play a huge part in determining the writings that would have staying power as official canon, but those writings still predate the church itself.