It's not about rolling your own, but the amount of serious downtime they have had recently, probably overshadows the actual downtown that would happen without their protection. It's growing in popularity a lot and is protecting more than 20% of all websites now. It will probably grow bigger. Consequences will just grow and most developers keep ignoring the fallacies of distributed computing: https://en.wikipedia.org/wiki/Fallacies_of_distributed_computing
All the cloud vendors does a decent job at providing protection (WAF, etc.) and it's rarely, if ever in recent years, that you would have global downtime for the big 3 (Microsoft, Google, Amazon). Yet more and more are using Cloudflare in combination with these vendors, increasing their complexity and potential downtimes.
February, March, June, November, December... and December again.
Their practice and routines for rollout probably needs some refinements.