Managing risk comes into play here. Would you spend time integrating 2 services, negotiating 2 contacts, supporting 2 providers who may change features and approaches over time, splitting a fraction of traffic to make sure both still work, limiting yourself to common feature set... Or would that cost you more to implement them a few days of (potential) complete downtime.

Choosing the potential downtime is not a failure, if you considered your options.

You have to admit that the Smyte's customer list that's floated around, here, isn't all just some startups that can't afford to research their backups. And maybe they did, actually. Did anyone even hear if Zendesk was even affected by this happening?