Right, but Cloudflare doesn't have to pay for it in that case. If Cloudflare sends you to their Indian POP, then they have to pay their Indian service provider for traffic. If they send you to their France POP, then they have to pay their French ISP for traffic. The Indian provider cannot claim any of Cloudflare's traffic in that case, because the Indian service provider wouldn't have any relationship with Cloudflare
This is very standard for places with high ISP costs, like South Korea and India. You can see a lot of discussion about it online. I agree with you that Cloudflare should be more transparent if / when they make different routing decision for Free/Pro plans based on bandwidth costs, but I don't think their decision itself is unreasonable at all. Indian bandwidth is very expensive.