Simple; the Bush Administration's approach to regulation was to "let the industry police itself". So when left to their devices, they of course reduce standards so they can generate securities to sell. Conservatives always think that capitalism works in benevolent ways, but it doesn't. Capitalism is not benevolent and never will be. Capitalism will seek to achieve profits by any means necessary. In this case, those means were to issue a flood of subprimes, coupled with a laissez-faire attitude toward regulation, to create securities to sell on the secondary mortgage market. That's what they wanted to do and Bush let them do that a number of ways; chief among them is letting the industry "police itself" which someone linked to earlier in this thread.
No, the CRA was not a factor in the subprime lending. Only 1 of the top 25 lending institutions from 2004-7 were subject to CRA rules. CRA loans also performed much better than non-CRA loans. Also, the CRA does not apply to non-bank lenders, who were the overwhelming majority of lenders who issued subprimes.
When it came to "selling of the risk", that's where the ratings agencies came in and faked better ratings on securities in order to increase their value on the secondary mortgage market. Again, this is a consequence of "letting the industry police itself" since ratings agencies are so closely aligned with the banks.
As for the actual requirements on the borrowers, this is where no-doc and NINJA loans come into play. Those loans, issued by non-bank lenders largely, were not subject to CRA requirements and were the "low standards" you're seeking.