A couple of reasons:

- The free CDN is basically unusable with my ISP Telekom Germany due to a long-running and well documented peering dispute. This is not necessarily an issue with Cloudflare itself, but means that I have to pay for the Pro plan for every domain if I want to have a functioning site in my home country. The $25 per domain / project add up.

- Cloudflare recently had repeated, long outages that took down my projects for hours at a time.

- Their database offering (D1) had some unpredictable latency spikes that I never managed to fully track down.

- As a European, I'm trying to minimize the money I spent on US cloud services and am actively looking for European alternatives.

You don‘t have to get the Pro plan to solve the Deutsche Telekom issues. You can also use their Argo product for $5/month - but only makes sense if your egress costs wouldn‘t exceed the pro plans pricing.