Requirements are dangerous
Software architecture it's much more than satisfying requirements. Requirements can be tricky and several times misleading. Requirements are easy answers and they often shut down important discovery processes. Requirements are old as snakes, they were heavily praised by RUP, CMMI, PMI and still in vogue nowadays. The requirements list is just a wish list someone made. Requirements gave the false sensation of doing the right thing but this is just a lie. Requirements are often lying. Software architecture is a continuous process that requires thinking, judgment, leadership, and critique. Requirements are some easy to be gamed and often they are. So why people do it? Well, I think thats the wrong question. Software is full of sudo-science being used for ages and just does not work like estimates for instance.