One-time pad offers complete security, but it has two major problems in practice:
 

First one is, one time pad requires a random key of length same as the original message.

this is where problem arises. making large quantities of random keys for any heavily used system might require million of random characters on daily basis. This presents an enormous challenge to provide truly random characters

Second one, and even more challenging is, distribution and protection of the private key.
as both sender and receiver requires the same key and protecting the key is equally mammoth task.

because of these issues, one time pad has a limited utility and used only for the low bandwidth channels.