I have a stupid question

[sanguals]

Pardon me for my ignorance, I do actually know little about any type of computer languages. But I know that some good programmes do really help sometmes. You may complete difficult works in a short minutes with "ready-made" programmes. Something like Menus, many products(Sothink DHTML/Tree Menu|Xtreeme DHTML Menu|SmartMenus DHTML) provide excellent ways to deal with them.
But there is one thing confused me(laugh at me PLZ): Why Developers prefer to do their works(like menus) by JS or AS rather than by those ready-made programmes? Developers kill their time by write the code by hand, even they know those programmes, even they see the download page(or google them), but never download any tools for help, why?