Software developer or bug developer

If a person who develops software is software developer, why not the same person developing bugs in the software be called bugs developer. How many developers ethically perform the unit testing after completing development of a unit? It could be – None, a few of them, some of them, most of them or all of them. Some of them might be under the impression that they perform unit testing after completing a unit but the way they do it might not be really helpful in finding bugs. It might be just to satisfy them what they do and call it as unit testing.

If developers really perform unit testing, find out the bugs and fix them, in actual, then when testing is being performed by the testers why they have to perform unit testing again? Why can’t the testers skip it and save lot of money and time of the organization.