Why is a large busy network more likely to use DHCP?

Answer 1

Because static routing requires someone to manual create a routing table for every subnet on the large network and the larger the network the bigger the margin of error in the routing tables

larger network also change more, more subnets are added ip are changes every time a router IP is changed or a new router is added a routing table need to be added to that router and the routing tables on other routers need to be modified so the other router know how to communicate with the new router

whereas dynamic routing learns the routes for its self saving human error and manpower

Answer 2

Because in a large network it would not be an effective use of IPv4 addresses to assign a static address to every unit needing one. Not to mention improbable for any portable devices like laptops.