Do you know of a registrar that doesn't do that?

Sure, that's what you're paying them for. Cloudflare is not a "dumb" domain registrar, they are an integrated service.

> Getting a TLS certificate is pretty quick

Most of the time, yes. Sometimes there are outages or whatever. It makes sense to just get it done ASAP.

Distributing that TLS certificate to their edge network may take some time as well, and who knows what other internal prep they need to do.

If you make a CAA record on Cloudflare then they add extra invisible CAA records which authorize the ~4 different CAs they use for CDN certificates. They really assume you're using the whole stack, not just DNS.