Why most unit tests are waste of time?

In my experience, unit tests are most valuable when you use them for algorithmic logic. They are not particularly useful for code that is more coordinating in its nature. 

E.G: An example of algorithmic logic is a pool of temporary numbers in a mobile phone system. The telephone numbers in the pool are used for routing calls in the network. Typically a request is made to get a temporary number, it is used for a few hundred milliseconds, and is then released again. While it is used, it is marked as busy in the pool, and when it is released, it is marked as free in the pool (and can then be handed out for another call). 

unit testing is an manual test which can took more time as comparied with test automation using selenium  webdriver

Writing the huge number of unit test for the sake of to test every thing might be the waste of time, but writing the unit test which give you more ROI in term of feed back ,time is a worth to write. 

Unit test is performed by Developer not by Tester