Why doesn't pbpaste return cursor at new line in bash?
pbpaste pastes exactly what you copy.

In your case you have copied the line not including the CR/LF at the end.
To get the return you need to copy from the start of the line to the beginning of the next line

From @patrix comment

Most commands do end with a CR/LF. e.g. echo "Hello" will put out a newline, however for echo this can be changed echo -n "Hello".

If you want you can add a newline after a pbpaste by using echo "$(pbpaste)" instead.