The simple answer of this question is this that selective breeding was an old method or process which take some months or even some years but genetic engineering is a new and most modern technology which can be done even in some minutes...

Selective breeding was the practise done earlier for man to get the traits which they wanted from an organism. It was the long process and had some limitations. While genetic engineering is the same of having different traits but by the new technology advancementsand with no limitations, and can be done in few minutes.