..if that's the case, I wonder why ISPs don't allow users to opt for dynamic addresses (at less cost to the ISPs), which, on the surface, appear to be more desirable for many (most?) users?
Because fixed IP addresses cost the ISPs more money. With fixed IP addresses each user has to have dedicated hardware allocations that cannot be used by any other users. With "leased" (dynamic) IP addresses 100 users may be served by as few as 25 or 30 IP addresses. Thus reducing the ISPs cost 70%.
My son and I have the same speed service (60 Gbps) from the same ISP but for business reasons he has a fixed IP address and I have a leased IP address. He pays $200 more a month for his internet connection. (Of course in the even of an outage the ISP provides my son with on the spot repairs on a 24x365 basis. I have an outage it can take 24 to 48 hours before a technician will appear at my location.)
