It says that banks that wanted to resell their loans to Fannie had to abide by the rules.
"However, in order for lending institutions to have access to the secondary mortgage market of Fannie Mae they had to abide by Fannie Mae's rules."
That's voluntary compliance.
Then this, in the summary:
"The lenders would not have written the flawed mortgages with their bobby-trapped conditions if they could not have counted on selling them to Fannie Mae or getting default insurance from such sources."
It still isn't the CRA that lead to the crisis. It was the greed of the banks and the ease in which they could pass off the risk (either to Fannie or as CDOs) that created the problem. Fannie gets some of the blame too. And so do the borrowers. And so does the federal government in general, for not being on top of this ****. But, again, it wasn't the CRA, since most subprime loans originated through companies not under CRA regulation.