Why after 2007 are prime and subprime RMBS treated as one asset type?

What will be an ideal response?

Prior to the crisis that occurred in the subprime mortgage market that began in the summer of 2007 and the subsequent housing market meltdown, private-label RMBS and subprime RMBS were viewed as two distinct products and traded in separate markets. However, due to the poor performance of the underlying residential mortgage loans backing both types of nonagency RMBS, the post-2007 market no longer makes a distinction between these two products. Thus, prime and subprime RBS are treated as one asset type.