sometimes its just more fun to do it yourself. you learn more about electronics. when you buy everything ready made you dont learn a lot. E.g im trying to transmit data at the moment i could easily go out and spend extra on a fancy transmitter that does manchester encoding and CRC but then i dont learn anything. it becomes just joining blocks of premade hardware onto each other which doesnt truley teach you electronics and doesnt help your engineering abilities develop because it requires minimal understanding