>>artifi+(OP)
I mean, 99% of the reason to have a domain with Cloudflare is their DNS/WAF/CDN and the options you get from having them at the edge. If CF isn’t handling your DNS they can’t provide those services without some very specific configurations that aren’t for the faint of heart.
You can use anybody as a registrar if you don’t want those tools though. CF sells domains at cost so it’s not something they aren’t making money on.