While Nvidia focuses solely on GPUs, AMD has a wide product suite. AMD has a wide reach in the computing industry with its embedded processor, CPU, and data center product lines. As a result, AMD becomes a proxy for the computing industry as a whole, not just in a specific GPU sector in which Nvidia has seen incredible growth.
While this hurts AMD during boom times, it also helps during downturns. This is evident in their revenue growth rates over the past three years, as the last year hasn't been great for GPU sales.