Again, there is no simple answer. It depends on situations and resources. Some systems might rely on multiple services. If those services are independent, in such system this might cause more frequent failures which might still result in serious outages even when only one service fails. For those kind of systems a single service provider might be more preferable, because a single provider might coordinate things more efficiently while with multiple providers you might wait longer until each one fixes its problem. For example, system A depends on system B. If both A and B depend on Cloudflare and Cloudflare has 1 hour outage, both A and B will have 1 hour outage. But if A and B depend on different providers, the situation might be similar for B but worse for A. This is because for A each hour of outage in any of the providers means 1 hour of outage. In such cases each additional provider might be an additional weak link.

> If you actually care for the resiliency necessary to survive a provider outage you should have more than one provider.

Well, that probably means duplication. This might be too expensive in certain situations. Also some occasional outages might be not a big concern for some, such as most bloggers.

I'm not downplaying the downsides of centralization. Certain things should be decentralized if it's reasonable. But it's not always that way.