The Internet is not as redundant as you might think, and in fact there is less spare capacity to go around as a result of the pandemic (a lot more time spent streaming and on video chats by a larger number of people). Internet routing is also non-trivial (convergence has not been reached in years), and when a major link goes down it can take time for routes to stabilize. Also keep in mind that the Internet itself was not down for most people who were affected by this; rather, connectivity between users and various services was affected. So people could have continued torrenting, but their Zoom sessions would get dropped because connectivity to some data center was impacted.