So if you need that package in your 10 projects, do you copy those 20 lines of code in your 10 projects? Yikes. Then what happens when it requires a change? Do you make the change in all your projects? Double yikes. When it becomes 30 lines, do you still copy/paste those 30 lines in all your projects? Do you also copy/paste the tests related to those 30 lines in all your projects? ...

Having reusable code wrapped into packages is basic software engineering.