Because there are few architecture assets. In fact, the first execution of the ADM will often be the hardest, since the architecture assets available for re-use will be relatively scarce. Even at this stage of development, however, there will be architecture assets available from external sources such as TOGAF, as well as the IT industry at large, that could be leveraged in support of the effort. Refer page 84 (section 5.1) of TOGAF 9.1 PDF.