A second ISP isn't free, it has significant costs in terms of dollars and complexity. The question is, does CF and another provider have significant benefits to justify the additional costs? For it to make sense you have to believe the redundancy CF provides is significantly lacking (and in a way that adding a second provider addresses). Maybe it's true, but it would be nuts to just assume it and start spending a lot of money.
That’s certainly possible in specific cases, but not a very good general principle to rely on. One CF could very well be better than two given ISPs.