Of course is the architecture and the creator of such a thing, isn’t the point of a tool like that for users that don’t have the tech knowledge? I have only used those systems on shared hosting, host providers are the one maintaining and should be keeping them up to date and WHM/Cpnel have plenty of customers to worry too patch holes, if they can’t then who’s fault is it, Architecture, or provider? Hope is the customers fault?

I would worry less about big shared hosting providers, who have a strong interest in patching their stuff quickly, than the market of people who get one or two dedicated servers or KVM VMs and then install cpanel on them and for the rest of the time they use it, ignore the CLI of the servers and never patch anything. There's a lot of small users of cpanel that have just a few licenses.