Originally, SSL certificates required a dedicated IP addresses due to limitations in the SSL/TLS protocols and thus we included a dedicated IPv4 address for free to all customers purchasing commercial SSL certificates from us.
However, this all changed with Server Name Indication (SNI) which allowed multiple SSL certificates on the same IP address. We have supported SNI on our hosting servers since at least 2016 and it has been ubiquitous across web browsers for quite a while, with anything that doesn't support SNI also not supporting modern cryptographic standards and thus not able to connect securely anyway. This essentially means that dedicated IP addresses have not been necessary for sometime.
With this in mind Freethought no longer includes a dedicated IP address for free with SSL certificates, and in order to preserve limited supplies of IPv4 addresses does not make the option readily available. Where there is a strong technical requirement for a dedicated IP address then one can be provided at a cost by contacting support.