I guess they only care about video. But for websites multi-CDN means essentially building your own CDN where using other CDNs isn't even a good idea, since they

I guess they only care about video. But for websites multi-CDN means essentially building your own CDN where using other CDNs isn't even a good idea, since they don't provide enough granularity of control to monitor and choose nodes and therefore limit you in what you can achieve in terms of latency and availability. DNS is also your biggest and often the only friend here, learning and deploying it yourself is critical, don't rely on any vendor to do it.