Because their main network all uses one big IP address pool and the blocks by various regions/countries against their site were probably not just DNS blocks but also IP address blocks.

So they now have an account whose activity is getting their IPs banned in countries where they operate.

So they told the account owners they needed to pay for an enterprise account and a dedicated IP address pool maintained by cloudflare. That's why CF kept talking about BYOIP in the emails.

i.e. "Pay for us to build you a quarantine with your own IP pool or leave ASAP"